Simplify Harmonic Notch setup process #7986

This discussion in the 4.7 category reminded me that I'd like to clean up our harmonic notch setup wiki pages.

I think we have these pages (at least):

• Managing Gyro Noise with the Dynamic Harmonic Notch Filters
• In-Flight FFT-Based Harmonic Notch Setup (child of the above page)
• Raw IMU Logging for FFT Analysis (over in the logging section)

They key problem is the pages do not make it clear to the user the steps required to complete the harmonic notch setup. I think a well written wiki page allows the user to start at the top and slowly work their way down making choices along the way as the docs point them out and finally arriving at a well setup feature.