plugins: add metainfo for all available plugins

Reference: https://bugzilla.gnome.org/show_bug.cgi?id=731676
Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>
appdata: Escape ampersands in AppData XML

Otherwise the XML is invalid and intltool will complain.

https://bugzilla.gnome.org/show_bug.cgi?id=731676
Switch to intltool's native GSettings support

Allows coexistence between GSettings and AppData files.

https://bugzilla.gnome.org/show_bug.cgi?id=731676
exif-display: Fix stock icon usage
exif-display: Convert deprecated GtkTable to GtkGrid
Post-branch version bump