Add trade history levelDB, trade_MP call, clean up MetaDex populateRPCTransactionObject

1) gettransaction_MP now works for any metadex order not just open ones
2) populateRPCTransactionObject now parses off the wire for metadex just like all other types
3) new levelDB MP_tradelist
4) every *completed* trade added to tradelistDB with txids, addresses, properties, and amounts
5) new gettrade_MP call added
6) gettrade_MP will iter metadex map to determine if offer still active
7) new getMatchedTrades function added using tradelistDB to return all trades matched with a supplied txid
8) gettrade_MP will call getMatchedTrades and supply to user over RPC
9) mscrpc 7 function to dump tradelistDB

example
http://pastie.org/pastes/9698921/text?key=a5n5cqglbd80c7tfytwgxw
Redundant. Seems to create a build warning:

> mastercore_rpc.cpp: In function ‘int populateRPCTransactionObject(uint256, json_spirit::Object*, std::string)’:
> mastercore_rpc.cpp:1532:10: warning: variable ‘offerOpen’ set but not used [-Wunused-but-set-variable]
>      bool offerOpen = false;
>           ^