Compute and add median per-FMA response times for medical vs. fire

[futurechris]

• [x] Compute median response times for both types
• [x] Add them to fma_api_rollup table as two new columns

Basically create a notebook with these calcs, put it in the analytics branch with comments about how it became our final data, noting any decisions we made about how to handle data/outliers.

Might be useful to roll the original combined-medical-fire data computation in this notebook, if it isn't already in the repo.

[futurechris]

Ended up also re-calculating the 'overall' median per-FMA response times, to make all three have the same normalizations/cleaning/etc.