Improved CLI

Godeps: bump github.com/ethereum/ethash

This fixes the build.

It is now possible to exit the REPL using Ctrl-C, Ctrl-D or by typing "exit".

The ethereum command line interface is now structured using subcommands.
These separate the different tasks it can perform.

Almost all flag names are backwards compatible.

The key tasks have not been ported to subcommands since they will be
replaced by the new accounts infrastructure very soon.

It is no longer imported by any package in our tree.

Various functions throughout the codebase used it to grab settings. This
has to stop because I want to use them without reading the config file.

These functions can now be used without reading the config first:

* ethdb.NewLDBDatabase
* ethrepl.NewJSRepl
* vm.New

Merge branch 'develop_pull_request' of https://github.com/tendermint/ethermint into tendermint-develop_pull_request

Add initial implementation of block tests

* Add blocktest cmd and support for block tests files in
  tests/BlockTests , the launched node does not connect to
  network, resets state with a genesis block from the test file
  and starts the RPC API

It is unused and untested right now. We can
bring it back later if required.

Until chunked frames are implemented we cannot send messages
with a size overflowing uint24.

They got lost in the transition to rlpxFrameRW.

With RLPx frames, the message code is contained in the
frame and is no longer part of the encoded data.

EncodeMsg, Msg.Decode have been updated to match.
Code that decodes RLP directly from Msg.Payload will need
to change.

This mostly changes how information is passed around.
Instead of using many function parameters and return values,
put the entire state in a struct and pass that.

This also adds back derivation of ecdhe-shared-secret. I deleted
it by accident in a previous refactoring.