Standard edit pages unaccessable, provide a link

With a huge vocab, Taxonomy Manager is the only way to edit terms. Trying to edit a term via the taxonomy module means listing all terms, which leads to out of memory errors.

However, because Taxonomy Manager builds forms in a very weird way, other modules can't hook into it which means we need to be able to access the edit page via the normal taxonomy module interface.

For the moment, this patch provides a link to jump to the taxonomy modules edit page.