Rename top-level interfaces

• register -> registerContractForSettlement

• validate -> validateContract

• simulate -> calculateMaturationOutcome

• build -> compileContract

• create -> createContract

• createUnsafe -> createContractUnsafe

• hashParameters -> createContractHashes

• broadcast -> broadcastTransaction

• Mark several functions as private

• Add several debug statements

TODO:

• Replace balance() and findContractCoins() with getContractFundings()
• Rename payout/mature/liquidate

^ These will be done as part of #153 (closed)

Progresses #47 (closed)