* Wayland-background-dialog: fix memory leaks

* Wayland-background-dialog: check that the image is valid before using it

*Reduce the scope of the preview box

*Do not read the same value from gsettings before reading it from the color style combobox

Move image and colors labels, filebutton to left side of dialog

*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

*When icon positions are locked, do not show "Organize Desktop by Name" in the desktop context menu

* 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