Add support for more octoprint events

[Cadair]

Ideally, we would allow configuration of any valid event through the web UI. But at least configuration of any event through the config file should be possible. We will probably want to pass the whole event payload through into the template.

[Cadair]

Allowing configuration of generic events in the config file works, but some events probably have different data in the payloads which currently is not exposed.

[hieronymousch]

Thanks for your great plugin. I would love to see a heartbeat with temperature of the bed & nozzle...

[Cadair]

Thanks!

By heartbeat you mean just a message at a given time interval? Irrespective of if a print is running etc? I don't think there is an actual octoprint event for that? If there isn't an octoprint event can you open a new issue for the feature?