backgroundMenu: Release the click gesture if a grab operation begun

If an active grab on pointer events happens during multi-touch operations,
all non-pointer-emulating touches will be muted. This may leave the
Clutter.ClickAction incomplete if triggered by one of those sequences,
just to have a gesture take over and trigger a compositor grab, which would
leave the capture-event handler stuck eating events.

So listen for grab-op-begin from the display, and ensure the action is
released if such grab begins.
and the capture event handler stuck.
viewSelector: Add left edge drag gesture to show the app picker
viewSelector: Show the overview on 3-finger pinch gestures
windowManager: Switch workspaces on 4-finger drag

The workspace to switch is obtained from the direction received
by the WorkspaceSwitchAction gesture.
windowManager: Switch the focused application on 3-finger hold + tap

The gesture action only cycles through the applications in the current
workspace.