shell: fix various interactions with the minimized state

shell: fix various interactions with the minimized state

This fixes the following :
- if a surface was set fullscreen, and then minimized,
the fullscreen compositor state would stay on and display
a black screen ;
- if a surface was set fullscreen, and we would then
cycle between surfaces (with Mod+Tab e.g.), the fullscreen
compositor state would stay on, and the fullscreen layer
would sometimes hide surfaces positioned behind it ;
- style and functional polishing.

Change-Id: Ieeec480d16769f27d2ed7a97eb943e0100efcd0b
Bug-Tizen: TC-1349
Origin: http://lists.freedesktop.org/archives/wayland-devel/2014-July/016257.html
Author: Manuel Bachmann <manuel.bachmann@open.eurogiciel.org>
Author: Nicolas Guyomard <nicolas.guyomard@open.eurogiciel.org>
Signed-off-by: Manuel Bachmann <manuel.bachmann@open.eurogiciel.org>