qml: fix incorrect placement of mouse areas in various delegates

I believe that it is incorrect to place mouse areas within either background or contentItem.

First, we need to avoid using MouseArea in Control where it acts as the main mouse handler. For dragging, maybe DragHandler can be a substitute.

Second, the main mouse "handler" needs to cover the whole control. This is against the notion if it is placed under background, or contentItem.

Note that, this patch causes visibility cycle in GridItem due to MouseArea being moved out of the parent-child chain.