Major changes to how torrent updates between daemon/client

This changes how torrent updates are sent to clients as well as
improvements to the ui update routines to make it faster. The
clients cannow ask for only the updated torrents being sent,
which makes it possible to only update the necessary torrents in the UI.

* GTKUI now asks only for changed torrents
* Added torrentfilter.py to sessionproxy which handles filtering
* Added PyDBLite (wtih SQLite support) too filtermanager.py and torrentfilter.py