Wrapper: investigate cache invalidation strategy for app info

[sohkai]

With the caching introduced in https://github.com/aragon/aragon.js/pull/176 (with no cache invalidation), we may run into problems with the cache becoming too big.

In particular, leaving a client running for a long period of time and browsing a large number of DAOs will fill the cache with unnecessary memory unlikely to be used again.

Some ideas:

• Fixed size LRU cache

[sohkai]

aragonUI now has a cachedMap utility that implements a simple LRU cache