This component will let the developer access different parts of the
QAbstractItemModel implementations that are impossible to be accessed
from QML. i.e. columns!=0 and the tree branches.
REVIEW: 106272
We need this in some components to work around weaknesses in the
standard MouseArea (such as conditional accepting of events).
MouseEventListener basically provides wiretapping for mouse events,
without blocking them, so they are still effective in the underlying
widgets.
