When we restart the signal server, the client might reconnect and still
think it has state (i.e. is on a frequency). We should fix this in the
client, but meanwhile we can just send out a leave to a client if they
request to leave a frequency, even if they are not currently on a
frequency.
We can now autoconnect via parameter on web, e.g. `freq=430.200`, which
then autoconnects to that frequency, creating it when it is not already
created. We also now reconnect on connection failure and display the
connection state down below.
We now send out messages to all participants at the same time (or more
or less, as asyncio permits). To not fail in case we can't send the
message to one player, we ignore send-exceptions in these occasions and
hope that the `for data in self.websocket` in _handle_client() will
throw an error and kick the client out of our game.
Sebastian Lohff