move and rework SendMoney to rpcwallet

- as SendMoney is ONLY used in rpcwallet move it there
- also rework the function to not log errors but use throw JSONRPCError
- removes a check for IsLocked() that is done in sendtoaddress and
  sendfrom RPC calls already
- remove translations in SendMoney (never used in the GUI)
- cache GetBalance() return value, because it's possibly used twice
- fixes #3007
very minor include ordering cleanup for rpcwallet.cpp