Feature memoize votedetail

Calculating the votedetail is quite slow due to the way our ORM works. This stores the result of calc_votedetail_dict in memcache.

Cache invalidation *should* work, and from a quick testing it looks like it actually does, but I'd be happy if someone could give it a bit more testing. Thanks!

I'd like to merge this ASAP, as this is a current problem in an angoing problem.