Add BUN/creatinine Chart

[pburnsdata]

Per email from Jim:

I have wrapped up a draft of the clinical workflow, but in doing so I realized that there is one additional display that would be great to be able to have when we launch: a graph of BUN/serum creatinine over time, with two threshold lines, one at 10 and one at 20.

Step 1: is BUN/creatinine in data....

[pburnsdata]

if not in test data, derive ahead of app