Use actual hostname instead of abbreviated host/site parameter

[banksJeremy]

Instead of use abbreviated host/site identifiers, we could use the actual host/domain names of the site. SEChatWrapper(host='stackoverflow.com')

This would allow some of our logic to just use the host value directly, instead of needing to translate from the abbreviated values.

For backwards-compatibility, we can accept the abbreviated names for now, but trigger a DeprecationWarning.

(If completed, I won't merge this directly into master; I'll leave it for @Manishearth to review.)

[Manishearth]

The reason for the multiple different login methods was that MSE/SO don't require a separate ping to SE.com/chat-login, logging into the site directly logs you in to chat. But if you can make this work sanely, that would be good :)

[banksJeremy]

There's still a special-case for stackexchange.com's login, but the rest of the login conditional chain is now:

        self.br.loginSite(self.host)

        if self.host == 'stackexchange.com':
            self.br.loginChatSE()

loginSEOpenID still sets fkey, because it's available in the post-login page, but for others hosts we don't immediately call .update_chat_key() any more. The request will be made implicitly the first time .chat_fkey() is called, which could be immediately if the bot starts watching a room.