Add a show clock and auto-firing

[viomonger]

Groups will now have a set time based on a show clock. There needs to be a 'start show' button that starts the clock ticking. Groups can still be fired manually out-of-order/whenever, but groups with a clock time will be auto-fired when that time is reached on the show clock.

Features:

• the show clock needs to be pausable
• when paused, the clock time needs to be adjustable (forwards or backwards)
• when paused, the show clock needs to be resumable
• a resumed show will not auto-fire groups in the past (even if never fired, i.e. skipped by clock adjustment)
• a resumed show will re-fire groups in the future, even if already fired

For consideration:

• if music timing is not baked into the cloud, may want to be able to adjust clock time slightly while running (i.e. jump it forward or backwards by 0.1 seconds)

[viomonger]

Auto-firing will be performed by the server, which keeps the true show clock (emitted to clients).

Need to pause the show clock if all clients disconnect

Other instances where a running show clock will be automatically paused?