Restore dash stack order when messageTray animation is finished.

This correct a minor visual glitch, avoiding the dash to be above the top panel
as soon as it starts sliding down.
In overview, only change workspace in WINDOWS view.
Add dock placement settings in schema.
Add dock placement in pref.js.
Reload extension when positioning changes.
DashSlideContainer: implement sliding in all directions.
DockedDash: manage positining in all direction.

Merge _updateYposition and _resetPosition. Now staticBox use the actor position
and not vice-versa as before.
myDash: myDash actor handle multiple dock orientations.
myDash: dash handle different orientations.
PressureBarriers follow dock position.
Add position class to the dockedDashContainer.

.left, .right, .top, .bottom are added depending on the dock position.
myDash: correctly handle drag and drop horizontally too.
TMP - positioning css styles.
Popup menus follow dash positioning.
Add bottom running windows counters.