Only mac style actually indicated focus as we depend on a
focus rect around the text label for other styles.

Bonus fix: When setting the width of the check box
we would still use the implicit width in the style which
meant that items would overlap incorrectly

Change-Id: Ibb4dc92633fbc5fb200a35d1c0b04a297c7f8f42
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>