layout/shell: Reset split type of windows

layout/shell: Reset split type of windows

This change would reset to default (none) orientation when activating a
different window, than those split and currently active.

The use-case is that when activating a different window all previous
split ones would reset to their original state (none orientation), such
that when the user tries to activate any former split windows it would get
the window without being split plus the other active window in the same
time. IOW going back and activating an former split window would also
display the other window which would complicate things a bit.

Bug-AGL: SPEC-4839
Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Change-Id: I315d42b656962bf3f68f140466ab58429a0e972c