validate: Allow groups with the same name as interfaces in Implements
From the specification:
if the interface wishes to allow for details about the implementation, it should do so by specifying that implementers add a group in their desktop file with the same name as the interface (eg: "[org.freedesktop.ImageAcquire]")
Also add interface name validation using GIO.
Increases GLib requirement to 2.26.
Edited by Corentin Noël