configurable versions for WFS checks

[cezio]

WFS checks (getCapabilities) has 3 hardcoded versions to use (1.0.0, 1.1.0 and 2.0.2). This usually works, but some services may require very specific version to be passed. For example service may accept exactly 2.0.0; 2.0.2 will return exception:

[justb4]

We attempt to support all OGC-specified WFS-versions: http://www.opengeospatial.org/standards/wfs. GHC now supports all (3) IS (official) versions.

But if more versions are needed we may add them. The fixed values are for user-convenience, we like to keep those pre-configured version options, but maybe extend them. We are open for suggestions.