Server-side timer management

[jflamy]

Timer event processing needs review. The current design is based on the assumption that refereeing devices are directly connected to the athlete-facing screen, so that "down" is given instantly. In order to be faithful to what the athlete saw, the athlete timer was originally assumed to be a master timer and it would send the time warnings and time over events back to the server.

In fact, given that there is a lot of usage of the tablets and of the MQTT devices for refereeing, the proposal is to move back to a server-centric timer. For situations where server-side sound is used this would also be a simplification.

NOTE: some laptops have very laggy sound cards - meaning that even on server-side sound there is a delay between sound triggering and sound production (several seconds). For example, using a wireless interface to speakers, or a digital interface to speakers can do this. This is not something we control.