g-ir-scanner includes section docs as class/interface docs if the section name is equal to the lowercase type name.
Since all the documentation is in section blocks, rename them to match the type names.
https://bugzilla.gnome.org/show_bug.cgi?id=727776
The priority handling of clip is now handled by GESLayer itself, and
handling clip as a ordered list should be implemented in GESLayer itself
too, this way the user can decide to switch mode at any time instead of