Solves bug caused by wrong hover status reported on the dash actor.

Close issue #124.

It seems that in Clutter the mouse pointer remains linked to the previous actor
when moving to a non reactive one. The change-hover is triggered and the hover
updated but, calling later manually sync_hover on the actor causes the hover
status to be wrongly calculated. No hover-change sygnal is triggered actually.

This bug was introduced by making the workspace switcher non reactive
(880e8941f0daede4e251c1449a0863371387918a). Just remove the code calling
sync_hover and forcing a recheck of the hover status as not necesary anymore.
Bug fix: scrolling workspace break show/hide animation #109

Due to the workspace switcher having been set not reactive
(880e8941f0daede4e251c1449a0863371387918a), hover status is set to true even if
the mouse has left the dash triggering the hide animation. The animation was
then stopped by checking fot the hover status, but no new animation was
started. The bug is due to old code: previously the workspace switcher was
alwasys making the hover status false, and the bug didn't appear.
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.
ALso border and padding need to follow the dash positioning.
WIP: reserve space  for the dock in the diferent positions.

TODO: should correclty reset on extension unload.
Code clean. Aslo set dash width to zero.
Track structs of the main actor instead of the inner _box.

The border of the container was not taken into accoutn.