Show dash in overview search when dragging app icon.

Move code controlling dash visibility inside the different overview
viwSelectors in the dockedDash class. Correctly shows the dash whenever an icon
is dragged. Dash visibility control is going to be rewritten in the future.
Minor code cleanup.
Code cleanup: use proper time units in css transitions.

Also I think the delay was ignored before.
Correctly track fullscreen for a non toplevel actor.

Actors that are not marked as toplevel are not taken into account when updating
actors visibility on full screen change.