data: Support launching via DBus activation

This will be the preferred way of launching applications, so install a
DBus .service file, rename the .desktop file to use reverse DNS notation
and mark it as DBus activatable.
Using reverse DNS notation for the .desktop file is also a prerequisite
for using GLib's new notification API.

https://bugzilla.gnome.org/show_bug.cgi?id=710913
alarm: Add a unique id property to alarms

Notification buttons work differently in the new notification API;
rather than invoking a callback on the notification itself, they
will activate an application action.
This means we will need a way to unambiguously identify a particular
alarm, so add a unique id property to that purpose.

https://bugzilla.gnome.org/show_bug.cgi?id=710913
Port to the new GLib notification API

https://bugzilla.gnome.org/show_bug.cgi?id=710913