Determine entity namespaces for site using API

Remove hardcoded namespace numbers for 0 and 120
replacing them with values obtained via existing
siprop=namespaces query by new Namespace class.

Move namespace=0 title reparsing into ItemPage.

Description of class PropertyPage should not recommend
including namespace in the title as namespace is and was
already provided.

Change-Id: If7ca06adbb4b9932bba0abffc7588afcb320e934