Provide a tag-oriented view

[davep]

Allow viewing all of the user's tags in their own buffer, perhaps as a cloud or something similar (see also wordcloud.el), and if the user selects a particular tag, it opens (if it isn't open) or refreshes (if it is open) the pin list such that only those tagged with that tag show.

As part of this it would be a good idea to turn the tags visible when viewing a pin into links that do the same as above.