media-keys: Extract the MediaKeyType enum into its own header

This allows us to not include shortcuts-list.h in other files and thus
avoids the media_keys array being defined in more than one place.

https://bugzilla.gnome.org/show_bug.cgi?id=730765
xsettings: Remove support for multiple X screens

Support for this has been removed from mutter and gtk+ so there's no
point in having it here.

https://bugzilla.gnome.org/show_bug.cgi?id=730765
xrandr: Remove unused function

https://bugzilla.gnome.org/show_bug.cgi?id=730765
locate-pointer: Remove support for multiple X screens

Support for this has been removed from mutter and gtk+ so there's no
point in having it here.

https://bugzilla.gnome.org/show_bug.cgi?id=730765
locate-pointer: Replace deprecated gdk_window_get_pointer

https://bugzilla.gnome.org/show_bug.cgi?id=730765
daemon: Stop using deprecated GSettings API
test-plugin.h: Stop using deprecated GSettings API
keyboard: Stop using deprecated GSettings API