create an overview map panel
|Reported by:||bartvde||Owned by:||mpriour|
Create an !Ext.Panel which wraps OpenLayers.Control.Overviewmap.
Currently I've done this in an application without creating a specific class inheriting from panel, but the problem is here that the destroy method of the OpenLayers.Control.Overviewmap assumes the div is still there, however it is already removed by Ext so the destructor fails. If we create our own component, we will have more control over the destroy sequence.