cmd: implement preimage dump and import cmds

The parameter `rand` is unused in `PrivateKey.Decrypt`. Decryption in
the ECIES encryption scheme is deterministic, so randomness isn't
needed.

core: minor evm polishes and optimizations

Fix issue unmarshaling single parameter events from abigen generated go code #16208

* build: add GOBIN to PATH for gomobile

* build: install gobind alongside gomobile

* crypto/bn256: full switchover to cloudflare's code

* crypto/bn256: only use cloudflare for optimized architectures

* crypto/bn256: upstream fallback for non-optimized code

* .travis, build: drop support for Go 1.8 (need type aliases)

* crypto/bn256/cloudflare: enable curve mul lattice optimization

accounts/abi, core: add AddTxWithChain in BlockGen for simulation

containers: drop vagrant support, noone's maintaining it

rpc: enforce the 128KB request limits on websockets too

* eth: update higest block we know during the sync if a higher was found

* eth: avoid useless sync in fast sync

Allow any vhost for wallet deployed by puppeth

common/compiler: remove "--add-std" arg, deprecated in solidity 0.4.21

travis, Dockerfile, appveyor, build: bump to Go 1.10

* cmd, dashboard, ethdb, vendor: send iostats to dashboard

* ethdb: change names

* ethdb: handle parsing errors

* ethdb: handle iostats syntax error

* ethdb: r -> w

* vm: optimize eq, slt, sgt and iszero + tests

* core/vm: fix error in slt/sgt, found by vmtests. Added testcase

* core/vm: make slt/sgt cleaner

internal/ethapi: make resent gas params optional

* cmd, dashboard: remove custom assets, webpack dev server

* dashboard: yarn commands, small fixes

vendor: bump duktape to get rid of build warning

core: should enqueue the invalids tx anyway