* les: move the checkpoint oracle into its own package

It's first step of refactor LES package. LES package
basically can be divided into LES client and LES server.
However both sides will use checkpoint package for
status retrieval and verification. So this PR moves
checkpoint oracle into a separate package

* les: address comments

* consensus/ethash, params: implement eip-2384: bump difficulty bomb

* params: EIP 2384 compat checks

* consensus, params: add Muir Glacier block number (mainnet,ropsten) + official name

* core/forkid: forkid tests for muir glacier

* params/config: address review concerns

* params, core/forkid: review nitpicks

* cmd/geth,eth,les: add override option for muir glacier

* params: nit fix

Also fix the input formatter on clique_getSnapshot and clique_getSigners
so that integers as well as hex number strings are accepted.

* build: use golangci-lint

This changes build/ci.go to download and run golangci-lint instead
of gometalinter.

* core/state: fix unnecessary conversion

* p2p/simulations: fix lock copying (found by go vet)

* signer/core: fix unnecessary conversions

* crypto/ecies: remove unused function cmpPublic

* core/rawdb: remove unused function print

* core/state: remove unused function xTestFuzzCutter

* core/vm: disable TestWriteExpectedValues in a different way

* core/forkid: remove unused function checksum

* les: remove unused type proofsData

* cmd/utils: remove unused functions prefixedNames, prefixFor

* crypto/bn256: run goimports

* p2p/nat: fix goimports lint issue

* cmd/clef: avoid using unkeyed struct fields

* les: cancel context in testRequest

* rlp: delete unreachable code

* core: gofmt

* internal/build: simplify DownloadFile for Go 1.11 compatibility

* build: remove go test --short flag

* .travis.yml: disable build cache

* whisper/whisperv6: fix ineffectual assignment in TestWhisperIdentityManagement

* .golangci.yml: enable goconst and ineffassign linters

* build: print message when there are no lint issues

* internal/build: refactor download a bit

This PR implements the LES server RPC API. Methods for server
capacity, client balance and client priority management are provided.

* les: loose restriction of unit tests

* les: update unit tests

* les, light: slim the unit tests

* les: rework clientpool

This change adds support for EIP-1898. 

* les: detailed relative cost metrics

* les: filter txpool relative request statistic

* les: initialize price factors

* les: increased connected bias to lower churn rate

* les: fixed clientPool.setLimits

* core: do not use mutex in GetAncestor

* les: bump factor db version again

* les: add metrics

* les, light: minor fixes

This change adds tests for the virtual clock and aligns the interface
with the time package by renaming Cancel to Stop. It also removes the
binary search from Stop because it complicates the code unnecessarily.

Most of these changes are related to the Go 1.13 changes to test binary
flag handling. 

* cmd/geth: make attach tests more reliable

This makes the test wait for the endpoint to come up by polling
it instead of waiting for two seconds.

* tests: fix test binary flags for Go 1.13

Calling flag.Parse during package initialization is prohibited
as of Go 1.13 and causes test failures. Call it in TestMain instead.

* crypto/ecies: remove useless -dump flag in tests

* p2p/simulations: fix test binary flags for Go 1.13

Calling flag.Parse during package initialization is prohibited
as of Go 1.13 and causes test failures. Call it in TestMain instead.

* build: remove workaround for ./... vendor matching

This workaround was necessary for Go 1.8. The Go 1.9 release changed
the expansion rules to exclude vendored packages.

* Makefile: use relative path for GOBIN

This makes the "Run ./build/bin/..." line look nicer.

* les: fix test binary flags for Go 1.13

Calling flag.Parse during package initialization is prohibited
as of Go 1.13 and causes test failures. Call it in TestMain instead.

* les: wait all task routines before drop the peer

* les: address comments

* les: fix issue

les: handler separation

* eth, interal, les: add getHeaderBy* APIs

* internal: address the comment

* eth, internal, les: getHeader nits, missing TD, console callable

This PR adds some hardening in the lower levels of the protocol stack, to bail early on invalid data. Primarily, attacks that this PR protects against are on the "annoyance"-level, which would otherwise write a couple of megabytes of data into the log output, which is a bit resource intensive.

* accounts, cmd, contracts, les: integrate clef for transaction signing

* accounts, cmd/checkpoint-admin, signer/core: minor fixups

* les: remove half-finish APIs

* les: remove half-finish APIs

* all: implement simple checkpoint syncing

cmd, les, node: remove callback mechanism

cmd, node: remove callback definition

les: simplify the registrar

les: expose checkpoint rpc services in the light client

les, light: don't store untrusted receipt

cmd, contracts, les: discard stale checkpoint

cmd, contracts/registrar: loose restriction of registeration

cmd, contracts: add replay-protection

all: off-chain multi-signature contract

params: deploy checkpoint contract for rinkeby

cmd/registrar: add raw signing mode for registrar

cmd/registrar, contracts/registrar, les: fixed messages

* cmd/registrar, contracts/registrar: fix lints

* accounts/abi/bind, les: address comments

* cmd, contracts, les, light, params: minor checkpoint sync cleanups

* cmd, eth, les, light: move checkpoint config to config file

* cmd, eth, les, params: address comments

* eth, les, params: address comments

* cmd: polish up the checkpoint admin CLI

* cmd, contracts, params: deploy new version contract

* cmd/checkpoint-admin: add another flag for clef mode signing

* cmd, contracts, les: rename and regen checkpoint oracle with abigen

* les: reject client connection if it makes too much invalid req

* les: address comments

* les: use uint32

* les: fix variable name

* les: add invalid counter for duplicate invalid req