Allows to fix backgrounds in Caja and fixes fading.
These changes somewhat break API behavior.

marco needs to get notified about animation updates.

This commit frobs the property to wake marco up.

https://bugzilla.gnome.org/show_bug.cgi?id=641526

Fixes https://github.com/mate-desktop/mate-desktop/issues/237

already mentioned in NEWS, just pulling the latest translations

- languages not present on Transifex
- languages present there but empty
- leftovers from gnome (with ancient translations and copyrights)
- en_US which isn't a translation

credits to Alexei Sorokin

It's not really necessary.

taken from:
https://git.gnome.org/browse/gnome-desktop/commit/?h=gnome-3-6&id=2738c5c

Now that we have a proper type for RGBA values,
we should use it (instead of packing the four components into a uint32).
https://bugzilla.gnome.org/show_bug.cgi?id=671750

taken from:
https://git.gnome.org/browse/gnome-desktop/commit/?h=gnome-3-4&id=0f60413

with help from Alexei Sorokin

it's not used anymore since this Caja fix:
https://github.com/mate-desktop/caja/commit/c74212b4630767b3b11b41cb26a8df20090096f4

When loading a picture to render it as desktop background, consider the presence of a rotation tag to display the picture properly.

Ported from https://github.com/linuxmint/cinnamon-desktop/commit/0a5f072befd97b6282a8cff71f0e184becf538b8