React to fontSettingsChanged inside diff editor

Change-Id: I72e5cd61ea67d87a3f82843ee1f3b42d13142dff
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Use minisplitter inside diff editor

Change-Id: Ia2388e8c50185f80111fcf96aedb8143088e9a1c
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Reviewed-by: Petar Perisin <petar.perisin@gmail.com>