WMS capability document of our extended getVSec

The XML document offered by the WMS Server does not contain the capability of our extended getVSec. This could be easily be added in the <Capability> <Request> section. This might contradoct the spec, though.

In addition (or in spite of above) we should add a couple of features to determine whether we can offer them to a WMS server as "VendorSpecificCapabilities", such as our stereographic projections and stuff.