Net_plugin first feature

Fix #34 - deterministic_randomness test failures

Fix dereference of DataStream struct

adds deterministic distribution functions for randutils
fixes shuffle to do deterministic shuffling
adds deterministic_distributions tests

I think I've implemented all of it, but it's not tested yet so I'm
leaving the issue open for now.

Define types, objects, and indexes necessary for proxied voting on
producers. Also, perform some necessary refactoring, as the old code
assumed the only way votes could be cast would be direct, not by proxy.

sbc is now named stake, and sys is now system, as described in
ROADMAP.md

It's still causing people build issues, and we can do better anyways.

up the minimum required boost level to 1.64 to fix problem with string::data() only returning a const char *

Now we calculate the round changes and store them in generate_block.

Progress:
- When an account adds/removes stake, we now update votes for its
approved producers
- Name map<AccountName, AccountName> as RoundChanges, and define
operator- such that RoundChanges = ProducerRound - ProducerRound

Test the vote updates, making sure that producer votes are updated when
an account adds stake

TODO: Calculate the producer round changes in generate_block and add to
block header

From where I'm standing, #35 is just due to the outdated genesis.json
and docs. Looks fixed to me.

Fix wasm_interface bug and other assorted changes

Add llvm dependency to Docker