Shorten dependency chain:
NetworkManager- -> NetworkManager-applet -> libappindicator3 /->/ gtk2-sharp -> webkit2gtk

- Split gtk2 and gtk3 builds using _multibuild. Python2 and Mono
bindings are only available for GTK2, so the GTK3 version has
significantly less build dependencies,
add only_require_python_for_gtk2.patch
- Drop dependency on deprecated gnome-common, see
https://wiki.gnome.org/Projects/GnomeCommon/Migration
- Allow configure run to succeed even when gtk-doc is not installed,
add make_gtk_doc_optional.patch