shell: Add implementation of fullscreen.
shell: Add implementation of fullscreen.

Undo fullscreen in shell_unset_fullscreen(), do all the stacking order
in shell_stack_fullscreen(), and configure black surface, method in
shell_configure_fullscreen().

Signed-off-by: Alex Wu <5fdd12daa1cc82d02f23966b88ca1b9fcb8b5a57@linux.intel.com>
Signed-off-by: Juan Zhao <bfd96be7c0d572ce6f47ceaf690b6d8daf94d540@linux.intel.com>

sir-murray/weston,eyolfson/weston,Gnurou/weston,Gnurou/weston,Fantu/compositor-spice,udoprog/weston,kwm81/weston,jonnylamb/weston,giucam/weston,jonnylamb/weston,mchalupa/weston,eyolfson/weston,mchalupa/weston,krezovic/weston,xorgy/weston,Fantu/compositor-spice,Tarnyko/weston-xdg_surface_present,xorgy/weston,udoprog/weston,Tarnyko/weston-xdg_surface_present,giucam/weston,sir-murray/weston,kwm81/weston,krezovic/weston,Fantu/compositor-spice