Add shared caches for Balrog public app

[bhearsum]

At the moment, the only caching we do at the app level is in-memory. This has two major drawbucks:

• We have to rebuild the cache whenever pods cycle up - which happens often
• The caches cannot be shared by multiple nodes - and there's no technical reason why they can't be

We could improve both of these things by adding memcache or something similar to the mix.

[jbuck]

I'd prefer to use redis over memcache, but this sounds like a good idea to me

[bhearsum]

I'd prefer to use redis over memcache, but this sounds like a good idea to me

I have no strong opinion, so let's say that unless someone has a reason not to :)