Add clear button and side action to customsortfiltermodel example.

Demonstrate the new side widgets feature of QLineEdit.

Change-Id: I1c4289c652abf2209e50601871249008fdec4f6b
Reviewed-by: Kevin Ottens <kevin.ottens@kdab.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
QNX: Prevent rendering when app is minimized

Windows will only be exposed and hence rendered when they are not
minimized. This will save useless computations and hence battery.

Change-Id: I83166cc6c3d89e878106c998a35890dd7788ed8a
Reviewed-by: Fabian Bumberger <fbumberger@rim.com>
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>