progress toward implementing 3x collateral + interest bidding
partial fixes
Update wallet market functions to use transaction_builder

NEEDS TESTING
charging interest on cover ops
Adjust short APR to be absolute rather than a percentage
paying interest on covers
Merge branch 'short-interest' of github.com:BitShares/bitshares_toolkit into short-interest
Update cancel_market_orders to use transaction_builder
Add wallet::create_transaction_builder

Simple utility function to create and return a transaction_builder.
Important if external code ever wants to use one, since the builder
needs a pointer to the wallet_impl, which is not available to external
code.
Merge branch 'develop' into short-interest
Enforce APR limit
Fix pretty printer for short list
Attempt to fix short list from chain_database (WHY DOESN'T THIS WORK??)

For some reason `this` is trash when I call my->_short_db.last() and I
get back an invalid iterator...
Fix bug in previous commit... somehow...
Fix order book wrt shorts
added ability to register public accounts and send funds to a public account
remove yield pool from supply for distributing yield
Merge branch 'short-interest' into develop

Conflicts:
	libraries/blockchain/include/bts/blockchain/market_records.hpp
Add hardfork warnings
Bump chain db version