BitcoinCLIClient, better handing of optional params

* Always remove null params in RPCClient.send()
* Clean up handling of null/optional in BitcoinClient
* First cut at BitcoinCLIClient (lowercase method names, optional parms)
getallbalancesforid_MP: Changed RPC types, return stronger type

* Handle current types returned by getallbalancesforid_MP RPC
* Return list of MPBalanceEntry types