Add module udiskie.tray

PyGTK status icon with popup menu for mount operations.
Add --tray option to udiskie daemon entry point

Shows the udiskie.tray status icon within the udiskie daemon mainloop.
Use force=True for lock/eject/detach in udiskie.tray
Fix tray to use associated drive for eject and detach
Yield only valid devices from Udiskie.get_all()

This protects from udiskie-internal race conditions when performing
actions on many devices.
Merge branch 'eject'

Conflicts:
	udiskie/udisks.py
Merge branch 'trayicon'

Optional PyGTK tray icon.