Redirect retrieval to internal function, and rename GConf to GSettings.

Turns out GSettings != GConf, who knew...
Rename gconf.py to settings.py, and add support for Wallpaper settings in GConf.
Try to detect the used Settings backend based on OS release
Merge branch 'feature/gconf-support' into develop
Bump version, update README, update changelog
Merge branch 'release/0.1.2' into develop