Version 0.4.2

Tidied up a bit.
Removed some unused modules.
Copied dir_monitor to rox-lib (will be removed in 0.5).
Get XDG_* variables from rox-lib (will be removed in 0.5).
Added argument side to Tray.add_box().
Methods Tray.remove_box(), Tray.clear_box().
Introduced Attribute descriptor, for fewer LOC in config classes.