Fixed GetWssIdForTerm to lookup the TaxonomyHiddenList in the rootweb of...

... the sitecollection

The GetWssIdForTerm method assumed to lookup the TaxonomyHiddenList in the current web. This issue popped up while trying to set default column values on a subweb, where the taxonomyhiddenlist was assumed to be available in that web. This fix looks up the list in the rootweb of the site collection instead.