[Feature request] Add beeper support

[Smeat]

Seems like we have some beeper code, but it isn't really used anywhere.

A solution would require the use of "vTaskDelay" or a similar approach, which doesn't use a busy wait (aka "delay") as well as the implementation of the "sound" message to disable/enable the sound.

[marcfon]

Would be nice to have an alarm when your battery voltage drops below a certain level.