This change ensures a scratchpad window is still centered on the screen
if it has first been shown on another screen of a different
resolution. Moving or resizing the scratchpad manually disables this
behavior.
Fix a crash that occured when moving a window to the scratchpad that is
seemingly floating to the user, but actually a descendant of a floating
parent con (and itself non-floating). If that is the case, move the
floating parent container to scratchpad instead of the window.
fixes#740
Sebastian Ullrich