Add LatLonBoundingBox for root layer

Adds a LatLonBoundingBox element to the root layer in the GetCapabilities response for WMS 1.1.1, and an equivalent EX_GeographicBoundingBox element for WMS 1.3.0.

According to the WMS 1.1.1 (section 7.1.4.5.6) specification:

"Every Layer shall have exactly one <LatLonBoundingBox> element that is either stated 
explicitly or inherited from a parent Layer."

The 1.3.0 spec contains a similar section (7.2.4.6.6).

We have a customer with a WMS client ([DigPro](http://www.digpro.se/index.php/en/?option=com_content&view=article&id=17&Itemid=46&lang=sv)) that is kind of picky and apparently refuses to work correctly if this element is missing.