dynamically add tag filter buttons

- based on all the tags stored in the database

Change-Id: I6a2ca7c740c836c0c82ff037d0a5be9dbf37481d
Reviewed-on: http://review.couchbase.org/23733
Reviewed-by: Ronnie Sun <ronnie@couchbase.com>
Tested-by: Ronnie Sun <ronnie@couchbase.com>