comments on preferences window

[Ulrik Sverdrup <ulrik sverdrup gmail com>]

Hi! I looked at your upstream-integration branch at github that you
pushed yesterday. I thought it's better to send comments as soon as
possible. Here is what I think. In general, it's great to see that
it's pretty simple to integrate a preferences window.. I have these
comments about the code, how it integrates with kupfer:

The .ui file is great

get_shared_data_dir: Not needed. We should use
config.get_data_file("preferences-dialog.ui") here instead;
get_data_file should be fixed to include installed DATADIR if it's not
in XDG_DATA_DIRS

preferences module looks fine, but should use the common kupfer
singleton idiom, not .get_instance() (see data.py's
GetSourcePickleService, GetSourceController => GetPreferencesWindow)

GconfStore: I don't know how it works yet, but in general, we
shouldn't hardcode anything, especially not in multiple places.

Style:
I know it's not common, but all of kupfer uses Python indented with
tabs. Set them to be four spaces wide if you want. We should try to be
consistent.

ulrik