Align FFT with vibration reference

[marselap]

Instead of (only) triggering FFT with a 1s timer, it should (also) be triggered with a new vibration reference. This is intended for vibration pattern accuracy analysis, but the regular 1s functionality should still be available for constant vibration references.

The code should then be running as follows: do the fft with 1Hz frequency. If a new setpoint arrives or a timer counts 1s, start new data aquisition. In case of setpoint-triggered fft, discard and cancel the ongoing process if existing/neccessary. Start the timer in both cases.