Test: make mouse press, release, click and double click default to the center of...

Test: make mouse press, release, click and double click default to the center of the item

Most of the times you just want to act on the item not caring the position.
This helps for cleaner test code

Change-Id: I0e8a4919c503e3fd6dee60e1bd937ac57622279f
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Reviewed-by: Christopher Adams <chris.adams@jollamobile.com>
Reviewed-by: Michael Brasser <michael.brasser@live.com>