Plasma/Multiscreen

without the ZUI, we need an alternate way to access the containments of screens that aren't connected...

the latest plan:

• when PVD is deactivated, we offer to purge the unused containments (but, in user-speak of course). other than that, we ignore PVD, because a virtual desktop can always be readded (whereas a screen may be physically unavailable).
• the activity manager UI will use thumbnails generated from the view (look at the code in kdelibs/plasma/animations/widgetsnapshot.cpp to see

how to do this). hopefully we can save these thumbnails out when closing an activity..

• when the current activity has >1 screen, it'll have a thumbnail for each screen. you can click to bring a containment to the current screen, and there'll be delete buttons for ones not in use.
• when a screen is detached its containment is left running as it is now; the performance impact of this should be negligible.