Add server-side caching to intensive queries

[hstove]

Some routes like /apps and /app-mining-apps are not fast. There should be a caching layer wrapped around SQL calls. Whenever an app is saved, the cache should be cleared, just like we trigger a cache clear on the front-end server.

[hstove]

@markmhx I'd propose with bump this up to a priority after finishing maker portal work - these APIs are only getting slower and it's even timing out at times, now.