Add QA scripts and improve docs for Key and KeyExtractor

[dbogdanov]

Add QA scripts for Key and KeyExtractor for evaluation on the existing key ground truth datasets.

Update the DOCs of these algorithms with the recommended settings for the prepreprocessing (missing to add high-pass filtering?).

Test impact of

• high-pass filtering
• detuning correction
• spectral whitening
• different profiles
  on accuracy on different datasets.

We can then write a blog post presenting this results and conclusions for the recommended settings.