wayland: provide window dimensions from prior to maxmize and fullscreen requests

This implements behaviour for the xdg_toplevel requests unset_maximized and unset_fullscreen according to the xdg_shell protocol documentation.

The xdg_shell protocol documentation states for unset_maximized:

If available and applicable, the compositor will include the window geometry dimensions the window had prior to being maximized in the configure event.

and for unset_fullscreen:

The compositor may include the previous window geometry dimensions in the configure event, if applicable.

Fixes #140 (closed), #620 (closed), #653 (closed), #792 (closed), #955 (closed), #1150 (closed), gnome-terminal#163 (closed)