There are missing parts to the "account-based" emotes that needs to be
completed before emote completion can be considered done. For now, when
I've been testing, I've been manually injecting the oauthClient and
oauthToken to the settings file with the `user_subscriptions` scope
* Add operator[] to ConcurrentMap which returns a TValue reference
* BTTV/FFZ channel emotes are now stored in the Emote Manager, and each Channel object has a reference to their own BTTV/FFZ channel emote map.
* Restructure EmoteManager a bit (simplify the ConcurrentMap havoc).
* Add EmoteData struct which can store emote data (for now only messages::LazyLoadedImage*)
* Add CompletionManager that does nothing
