* prevent removing active containments (brute force mechanism: just ignore the request totally)
* select the correct containment for removal when zoomed out (will have isses on multi-screen; see FIXME)
* move containment destruction logic out of Corona; it really doesn't belong there
* remove the hack to not set focus on a containment when clicked as that doesn't seem to reliably trigger it for me here and it doesn't address the issue of a new containment still messing things up, so we really ought to have a generic solution instead of a slightly ugly hack