Introduces WalletService object which is in control of
blockchain and wallet access.
The service manages a single transaction monitoring loop,
instead of multiple, and allows updates to the wallet from
external sources to be handled in real time, so that both Qt
and other apps (yg) can respond to deposits or withdrawals
automatically.
The refactoring also controls access to both wallet and
blockchain so that client apps (Taker, Maker) will not need
to be changed for future new versions e.g. client-side filtering.
Also updates and improves Wallet Tab behaviour in Qt (memory
of expansion state).
Additionally, blockchain sync is now --fast by default, with
the former default of detailed sync being renamed --recoversync.
AdamISZ