GDesktopAppInfo: support DBusActivatable

Support the sender-side of the freedesktop application specification for
cases that we find 'DBusActivatable=true' in the desktop file.

https://bugzilla.gnome.org/show_bug.cgi?id=699259
gio/tests: sort tests in the Makefile.am

...to make it clear where people should add theirs, reducing the chance
of conflicts caused by everyone always adding at the end.
Updated Galician translations