Allow to link to the list of all tags

Hi,

on my website, I have a cumulus tag cloud block that I do not want to link to the tag list of just certain vocabularies (as it can be controlled in the cumulus block settings), but the list of all tags, i.e. the /tagadelic page.
The attached patch creates a corresponding block option and modifies the link accordingly. I'd be happy to see this in the cumulus module.

Kind regards,
Tobias