main.py: Refactor code and use gobject introspection
main.py: Refactor code and use gobject introspection

We can use gobject introspection to use utilities such
as the notification service and modify gsettings. So
let's use those, and while we're at it, refactor the
code of the application.

Signed-off-by: Lucas Meneghel Rodrigues <75ff994d18a17892299c98a1dd68163bfb09a96f@gmail.com>

truongan/bing-desktop-wallpaper-changer,nks15/bing-desktop-wallpaper-changer,UtkarshGpta/bing-desktop-wallpaper-changer,UtkarshGpta/bing-desktop-wallpaper-changer,nks15/bing-desktop-wallpaper-changer