Also, update the gray mask that appears when user enters context of some
item. The mask is grown if the item changes its geometry, but never
shrunk, as this would introduce annoying flicker on the screen.

QMLObserver links against the library dynamically. User's apps can also
link to it statically, so that the app can be deployed with debugging
features to a device, without having to worry about library deployment.

This qmlviewer will be also the default one when opening qmlproject files
as the runconfiguration was changed too.