Added decorator-style properties to bugdir. Created settings_object module.

Added decorator-style properties to bugdir.  Created settings_object module.

settings_object.SavedSettingsObject encapsulates some of the common
settings functionality in the BE BugDir, Bug, and Comment classes.
It's a bit awkward due to the nature of scoping in python subclasses,
but it's better than reproducing this code in each of the above classes.
Now I need to move Bug and Comment over to *this* system ;).