Issue background jobs stats

Implementation of the background job for refreshing the cached functions from site stats in a regular basis.
This is a first approach and tries to be as simple as possible in order not to add complexity before it is needed (that will happen, of course).
Absolutely. The answer is that this is still a prototype. I would like to precisely define what needs to be warmed here, but for now I believe that the things that get warmed up in warm.py are the best option, yes.