window: allow moving maximized surface

Moving maximized surface will cause compositor to unsnap it
window-manager: pass correct flag to theme_get_location

We need to pass THEME_FRAME_MAXIMIZED to theme_get_location to detect
correct cursor position
shell: unsnap window when moving it in maximized state

This patch allows moving maximized surface through compositor binding.
When maximized surface is moved, its restored to its original size and
grab point is on middle upper part of the surface.
Merge branch 'maximize_fix_3' of https://github.com/rafalmiel/weston into next

Conflicts:
	src/shell.c
	src/xwayland/window-manager.c