Move to standard D-Bus integration for windows-service

Created by: ederag

hamster.desktop (and stuff currently handled by hamster-windows-service) should be improved to comply with https://wiki.gnome.org/HowDoI/DBusApplicationLaunching

Only the database server part (hamster-service) should stay separated.

The current hamster-windows-service (org.gnome.Hamster.WindowServer) is legacy, the main app (hamster-cli.py, installed as hamster), should replace it, since it holds a gtk.Application with the same id (org.gnome.Hamster.WindowServer): https://github.com/projecthamster/hamster/blob/4417b73334e5c34ae6c6998b5523fbccaf3568f7/src/hamster-cli.py#L92-L97

wip: #536