travis, Dockerfile, appveyor: bump to Go 1.13

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.

core/state: optimize some internals during encoding

core, metrics, p2p: switch some invalid counters to gauges

common, graphql: fix hash/address decoding + UI content type

* Accounts in alloc field must already exist

Note that accounts in alloc field must already exist, as pointed out by Simeon Vanov in https://gettoshare.com/2017/10/30/how-to-use-genesis-json-alloc-property/

* Change wording per PR review comment

* README: minor fixups

Dockerfile: expose GraphQL ports

Currently light.maxpeers is 100 - after this change it's 10 for non-servers.

Fixes #19820

internal/ethapi: implement fillTransaction

eth: disallow overwrite files via admin.exportChain

* les: wait all task routines before drop the peer

* les: address comments

* les: fix issue

* Change chainId in genesis block to 8888 from 0 

Change chainId in genesis block to 8888 from 0 per Moriteru in https://ethereum.stackexchange.com/a/28082/40230.

* Replace 8888 with “<arbitrary positive integer>”

Per PR review, replace Moriteru’s arbitrary positive integer 8888 with “<arbitrary positive integer>” in chainId field.

cmd, core, eth, les: support --override.istanbul

core/vm: enable istanbul EIPs in the jump table

This change adds support for gzip encoding on HTTP responses.
Gzip encoding is used when the client sets the 'accept-encoding: gzip' header.
Original change by @brianosaurus, with fixes from @SjonHortensius.

Original change by @jpeletier 

This copies cli.printHelp but changes minwidth to 38. Custom flag
code is improved to print the default value using cli.FlagStringer like
all built-in flags do.

build: gomobile automaticall adds the ios tag, don't duplicate

- Move the existing tests from memorydb into a generalized testsuite
that can be run by any ethdb backend implementation.
- Add several more test cases to clarify some non-obvious nuances when
implementing a custom ethdb backend, such as the behaviour of
NewIteratorWithPrefix vs NewIteratorWithStart.
- Add leveldb to the testsuite using in-memory storage for fast
execution.

* core: log chain reorg/split metrics

* core: report 1-block reorgs on the metrics too