This is done in a way which should simplify abstracting it to other
types of accounts if needed in the future
Remove comment about removing singletons - we're keeping them (and probably restoring some)
IrcManager now updates its "account" reference automatically through the
AccountManager.Twitch.userChanged-signal
Remove unused IrcManager getUser-method
IrcManager::beginConnecting is no longer called asynchronously. This
might want to be reverted in a more controlled asynchronous manner.
User Accounts are now stored as Shared Pointers instead of using
references/copies everywhere
