This series of patches merges in better support for hiding of surfaces

This series of patches merges in better support for hiding of surfaces

Essentially, this series modifies ecore_evas and evas engine code in
order that we do not need to destroy surfaces when hiding a canvas.
Previous code would destroy the wl_surface on ecore_evas_hide and have
to recreate it on ecore_evas_show. These patches eliminate the need to
do that by setting an engine field ('hidden'). When the evas engines
go to post a surface update, if it is 'hidden' then the code will just
attach a NULL buffer to the surface.

Merge branch 'devs/devilhorns/surface_hide'