Allow market_engine.cpp to be compiled as a stand-alone cpp file speed up compiles.  This involved creating a header file for market_engine.cpp as well as moving the class declaration for chain_database_impl into its own header file so market_engine.cpp could reference it.
Add /bigobj to wallet.cpp compilation flags on Windows
Merge commit '41eb4b7eed20f5ac1da3e70f218b3f37ce2f481e' into btsx

Conflicts:
	libraries/blockchain/chain_database.cpp
	libraries/blockchain/market_engine.cpp
Begin merging market engine
Move headers
Merge market engines