Small RDF patch

Hi,
  I notice that current svn master doesn't allow semantic items to be
created. Tracking this down it turns out that some method sigs have
changed and a template class still had the older sigs. The attached
patch allows one to insert a "Contact" semantic item with the editor
coming up to allow one to customize it. The context menu again also
allows editing semantic items. I put a quick shortout at the top of
addRelevantIDsForPosition() if there is *no* RDF so that there is as
little potential slow down in that case as possible.

  While I may be able to still commit using dev credentials I thought it
best to run by the list instead since I've been inactive on abiword for
a while.