Build a simulation mode for development

[joulupukki]

It’d be nice to have a mode where the software was simulating pitch detection so that one might be able to develop the UI and other tuner interfaces without needing to connect to an external preamp circuit or a guitar/instrument.

I think this could be done by generating frequency data on the fly from pitch_detector_task.cpp. The simulation mode could be enabled in user settings.

If the project had this, someone would only need an ESP32-CYD to make significant contributions.