[JRO] Omptimization on topics index

* Why was this querying twice for stuck and normal topics? Terrible.
  Removing "sticky" collection and just ordering by sticky first,
  updated_at second. Only one collection.
* Remove default scope on topic.
* Throw some partial caching around topic nav to reduce querying.
* Add not null constraint to several columns in topics table
* Remove unecessary attribs column in topics table