We now only open MIDI by default on non-Web platforms. On web, there is
an extra button to open MIDI devices. This allows us to no longer pester
users with the "allow MIDI" popup when they don't want to use MIDI.
If MIDI devices have been opened, the multiplayer part of this project
now uses it as well, in the same way the "singleplayer" part does it.
Move "Leave" buttons always to upper right of screen. The "Get a Wav"
button now has a text that expresses better what it does depending on
the platform (save, download, share).
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