QmlDesigner.PropertyEditor: Adding TabViewIndexModel

Adding this to the plugin for components.

Change-Id: Ia9612dc398f54880a3abd7142ca4096fa7aa1b7c
Reviewed-by: Marco Bubke <marco.bubke@digia.com>
QmlDesigner.Model: Fix help lookup

There is no need to replace anything. We just have to prepend ".QML".

Change-Id: I16ebfd1915ad7e879eb790acf3d69e880a313729
Reviewed-by: Marco Bubke <marco.bubke@digia.com>