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From where I'm standing, #35 is just due to the outdated genesis.json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

An account can now approve a producer, and that producer's votes are
increased appropriately. The account can remove approval, and the votes
are decreased appropriately. Additionally, the producer is added/removed
to the account's approved producers list as desired.

TODO: A producer with more votes than the rest is still never rotated in

Calculating the new producer schedule based on votes is now implemented;
however, the voting itself is not. :D But the code builds, and the tests
pass. It's good progress, it's been a good day.

Note that "the tests pass" means little at this stage, since I haven't
written any new tests to exercise the new code. In other words, NEEDS
TESTING!

- Rename config::ProducerCount -> config::BlocksPerRound
- Add new config::VotedProducersPerRound = 20
- Split up staked_balance_objects.hpp moving ProducerVotesObject to
producer_objects.hpp