This PR cleans up the CI build system and fixes a couple of issues.

- The go tool launcher code has been moved to internal/build. With the new
  toolchain functions, the environment of the host Go (i.e. the one that built
  ci.go) and the target Go (i.e. the toolchain downloaded by -dlgo) are isolated
  more strictly. This is important to make cross compilation and -dlgo work
  correctly in more cases.
- The -dlgo option now skips the download and uses the host Go if the running Go
  version matches dlgoVersion exactly.
- The 'test' command now supports -dlgo, -cc and -arch. Running unit tests with
  foreign GOARCH is occasionally useful. For example, it can be used to run
  32-bit tests on Windows. It can also be used to run darwin/amd64 tests on
  darwin/arm64 using Rosetta 2.
- The 'aar', 'xcode' and 'xgo' commands now use a slightly different method to
  install external tools. They previously used `go get`, but this comes with the
  annoying side effect of modifying go.mod. They now use `go install` instead,
  which is the recommended way of installing tools without modifying the local
  module.
- The old build warning about outdated Go version has been removed because we're
  much better at keeping backwards compatibility now.

* ci: tooltips for javadoc for mobile app

* f space

* build: remove env.sh

This removes the dirty symlink-to-self hack we've had for years. The
script was added to enable building without GOPATH and did that job
reliably for all this time. We can remove the workaround because modern
Go supports building without GOPATH natively.

* Makefile: add GO111MODULE=on to environment

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.

- Mime types generator (Standard "mime" package rely on system-settings, see mime.osInitMime)
- Changed swarm/api.Upload:
    - simplify I/O throttling by semaphore primitive and use file name where possible
    - f.Close() must be called in Defer - otherwise panic or future added early return will cause leak of file descriptors
    - one error was suppressed

* core/types, core/vm, eth, tests: regenerate gencodec files

* Makefile: update devtools target

Install protoc-gen-go and print reminders about npm, solc and protoc.
Also switch to github.com/kevinburke/go-bindata because it's more
maintained.

* contracts/ens: update contracts and regenerate with solidity v0.4.19

The newer upstream version of the FIFSRegistrar contract doesn't set the
resolver anymore. The resolver is now deployed separately.

* contracts/release: regenerate with solidity v0.4.19

* contracts/chequebook: fix fallback and regenerate with solidity v0.4.19

The contract didn't have a fallback function, payments would be rejected
when compiled with newer solidity. References to 'mortal' and 'owned'
use the local file system so we can compile without network access.

* p2p/discv5: regenerate with recent stringer

* cmd/faucet: regenerate

* dashboard: regenerate

* eth/tracers: regenerate

* internal/jsre/deps: regenerate

* dashboard: avoid sed -i because it's not portable

* accounts/usbwallet/internal/trezor: fix go generate warnings

* Makefile: add make swarm command

* Makefile: minor code formatting polishes

* Makefile: fix devtools target

* core: regenerate genesis marshaling with fjl/gencodec@cbfa5be5a8a8

* core/types: regenerate marshaling methods with fjl/gencodec@cbfa5be5a8a8

* core/types: add "hash" to JSON headers

* travis.yml: don't create darwin/386 builds

* build: remove godep remains

* internal/build: improve archives

- enable compression for zip files
- don't write half-complete archives

* build: add -unstable to archive names

This commit tweaks the debian packaging tool:

* All build environment metadata can now be overriden on the command
  line. This allows testing the CI build behaviour locally.
* -unstable packages now actually contain the binaries (oops)
* packages use Go 1.7 to build
* archiving is skipped for PR builds

The new build script, ci.go, replaces some of the older shell scripts.
ci.go can compile go-ethereum, run the tests, create release archives
and debian source packages.

Turns out we actually don't need it, USE_NUM_NONE works
because we also set USE_FIELD_INV_BUILTIN.

* changed stack and removed stack ptr. Let go decide on slice reuse.