Optimize HyperKitty database read operations

Archive View
* Fetch Ratings based on all ThreadIds
* Fetch Favorites based on all ThreadIds
* Fetch Tags based on all ThreadIds

Thread View
* Fetch Ratings based on ThreadId

* Add db_index to hyperkitty models

> How to migrate data from kittystore to hyperkitty store automatically? 
> Hyperkitty db now needs threadid in the Rating table, the info on threadid->messageid is only available in kittystore.

> On average roughly cuts the response time of Archive View in half, ~400ms to  ~200ms.

> South does not yet support Django 1.5 Meta.index_together 
> http://south.aeracode.org/ticket/1217