Implement reliable and complete app file open tracking

Method 1:
- hook on GtkFileChooser and implementations of recent files menu to introduce Zeitgeist events (done, gtk branch)
- hook on Nautilus (ongoing)
- hook on GNOME Shell (todo)
- trace back open()/write()/close() syscalls to validate opens/saves, etc through second event (todo)

Method 2:
- UDAC FileChooser which returns actual handles for openings or requires handles for saving, and logs Zeitgeist events
- UDAC Open, Close, Save functions in general
- virtual FS for apps (config, cache, tmp, etc)