Chat channel implementation

[rossengeorgiev]

This PR should be used to discuss the development of this feature. Continuation of #20, #21

Further changes via PR should point at chat_channel branch

[rossengeorgiev]

There are a couple of problems that have not been solved yet.

• When we join a channel, and reconnect, we are still joined, but every message we get will only contain the channel_id. So there is no way to reinitialize the ChatChannel objects from just that. The way Dota 2 does is a persistent file in the steam cloud. Even if we implement such a persistent file, any channels joined in the dota client won't appear on Dota2Client, or vise-versa. Perhaps, leave it like its now as any code will likely join to channels every time it connects.

• Channel member list for public channels is fetched over HTTP from dota2.com. The question, is whether it should let the code do it automatically (or on request). There is not much value in those members lists as they only contain names and channel_user_ids. Can't think of any useful usecase. Only spamming or mass reporting, so probably not worth implementing.