The monitors-changed signal was handled by the same function as
size-changed, which only redraws when the screen dimensions differ.
When a monitor is removed without changing the virtual screen size, the
desktop background was not repainted.

This adds a separate handler that always triggers a redraw, since
a monitor layout change requires repainting regardless of whether the
dimensions changed.

Fixes mate-desktop/mate-desktop#352

*Draw the background on the desktop window, using the same code as on navigation windows to bypass the no-root-window issue.
*Works from caja's "Change Desktop Background" menu item, from caja-extensions "set as wallpaper" and with changing the background in dconf-editor.
*All background options available in x11 supported in wayland, UI is new for wayland

*Apply changes immediately, keep the dialog open until closed by user
*Let users see changes in realtime while keeping the dialog open
*Preview both colors and pictures
*Add ability to apply changes from either combobox including using any image saved from when dialog was opened
*Add tooltips to the buttons, filepicker, and comboboxes

* Wayland: Support rendering the desktop

*Wayland support is optional via the --enable-wayland option

* eel-editable-label-c: remove unused variable

This was leftover from earlier code compatable only with x11

* Fix gtk-layer-shell-0 version check, improve error message when Wayland requested but not found

find . -regextype posix-extended -regex '.*\.(c|h|ac|txt|xml)' -exec sed --in-place 's/[[:space:]]\+$//' {} \+