New:

 - [transactions] Add order create/cancel and borrow operations with tests
 - [exchange] Allow for manual construction/signing and broadcasting of transactions
 - [account] new calls for BrainKey

Fixes:

 - [transactions] Do not deserialize String/json
 - [minor] changes
 - [types] Implement Map()
 - [exchange] Only use 'rpc' connection when really necessary
 - [price-feed] use default exchange sources if not defined in individual asset