Switch: add pressed-property and clicked() signal

Align with the basic functionality offered by CheckBox, and also
required by certain styles.

Change-Id: I53f2868f19a26e9abc0ed9c94d327edbe940429b
Reviewed-by: Caroline Chao <caroline.chao@digia.com>
ScrollViewStyle: expose scrollbar fade duration & delay privately

The Android style implementation will be able to set right values.

Task-number: QTBUG-35081
Change-Id: Ia3b51b867b04093a6c3caf3464be7e12d043d99f
Reviewed-by: Caroline Chao <caroline.chao@digia.com>