Introduce Utils::TreeView/TreeWidget

The only view that is sane is my view. Adds handling of return/enter
for macintosh. Allows for overriding whether single or double click
activates items via setActivationMode.

Change-Id: Id8f9001f99162833c682dfc5b2b1abac04ce18a3
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
PluginView: Use double click on all platforms for details

Change-Id: Ia48fd5ba352503dbc2686f961afee9754275fa55
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
SideBar: BookmarkView: Support Return/Enter on OS X

Change-Id: Iffbbf345f8ec2ce3152f9be38e6b05e372a7e4b9
Reviewed-by: Eike Ziller <eike.ziller@digia.com>