Add consensus perturbation signatures

[gwaybio]

My current plan is as follows:

• [x] 1. Process each plate independently (✅ in #34)
• [x] 2. Generate an across-plate consensus signature on broad_sample and dose.
• [x] 3. The consensus signature will be based on median and MODZ
• [x] 4. Output one single file for the full consensus signature
• [ ] 5. Output a separate file for a feature selected consensus signature (derived after calculating consensus)

Unifying documentation for this step from https://github.com/broadinstitute/lincs-cell-painting/issues/4#issuecomment-620839509 and https://github.com/broadinstitute/lincs-cell-painting/pull/34#issuecomment-629307961

[shntnu]

• [ ] 5. Output a separate file for a feature selected consensus signature (derived after calculating consensus)

You would not be able to do replicate_correlation selection on consensus profiles. You'd need to do this on the Level 4b data across all plates instead. But also note that when we do so, we first sample a subset of the plates to avoid inflating the report replicate correlations.

I'd skip 5. for now unless it is blocking

[gwaybio]

closed in #40