TableViewColumn: make resizing easier on touchscreens

Hitting the boundary between the columns is hard with a finger.

Change-Id: I1f2fd87dd87ec8f04dd3fbf4e58b7c6200bc493c
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Add missing tests for layoutDirection and mirroring

Change-Id: I8eaff4ba2a2a42c5ba01be9a96884ed851c6ee3a
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Make sure that layout is invalidated if LayoutMirroring is changed.

The old autotest never tested to see if the layout got rearranged if
_only_ LayoutMirroring got changed. (It was always tested together with
layoutDirection changes).

Change-Id: Ie541ccb101884b8d47770f32b4312bccd2329d47
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Make sure that items don't exceed the layout-computed boundary

When geometries were rounded to their nearest pixel grid geometry they
sometimes exceeded the area the layout calculated them to cover.
This could often be observed by that the visual spacing got shrunk to a
smaller size than was specified.
For small spacings values the visual spacing could even disappear.

With this fix the visual spacing should never be smaller than the
specified spacings value (but might be bigger due to rounding).

Task-number: QTBUG-36235

Change-Id: I5142c793460e50fd2de397abfd2ea6730f1bd042
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>