SplitView: wider splitter on touchscreens

7mm is a typical minimum size for anything meant to be touchable.

Change-Id: Ie29d178495f0b9feae7e76ceaed848301232d2b8
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>