Tagsets fixes

Many more automated tests added for tagsets. 

Fix for issue 2870: canonical associations causing errors on the review associations page
https://code.google.com/p/otwarchive/issues/detail?id=2870

Fix for issue 3754: tags with brackets can't be approved or rejected
https://code.google.com/p/otwarchive/issues/detail?id=3754

Specific test added for issue 3639, tags with unicode characters can't be approved
(This issue has been fixed by the Rails/ruby upgrade.)
https://code.google.com/p/otwarchive/issues/detail?id=3639