Make the desktop scripting activity aware:

adapt the desktop scripting from the time when Containment == activity to creating actual activities

* activities() -> desktops()
* activityById() -> desktopById()
* activityForScreen() -> desktopForScreen()

To create a new activity, there is the new global function
createActivity(activtyName, containmentPlugin (optional))

when you want to access the actual containments created by the activity, you do

Array[containments] = desktopsForActivity(activityId)