Added a real cache

Photo cache, the conversation view and people picker both use it.
Continue cache work

Added photo caching to the message view.
Added name caching

Now in the message list, we use the cache for names too.
Less queries to the service!
Removed duplicate caches.
Real user caching

I forgot to loop through the different users in each conversation, to
actually build a user cache!
Conversation list people caching
People are now pulled from the cache!