NCHK-2864: ePubCheck should emit a usage message when a non-standard nam...

...espace is used
@bmackenzie @apond 

Detect and report use of xml namespaces.  Code was already there checking for unused namespaces, so I added the usage message to the places where the namespaces were being first added to the dictionary.
Propagated the changes up to the callers and a lot of tests where these namespaces are in use but were not previously reported.   We suppress reporting on several default known namespaces, such as XML, XHTML, OPF, and OPS, etc, as they would only add noise and they are required for the file formats anyways.