add support for PAlt calculation

[jwildfire]

Add support for the new PALT measure derived here. Formula is below for reference:

test page

Test notes

• A new filter labeled ALT Elevated? appears in the Filters section of the controls with two options: No and Yes.
• Select Yes and verify that only those participants with a maximum ALT result greater than three times the upper limit of normal appear.
• Click a point and verify that the P_ALT calculation appears in the Participant Details section beneath the chart.
• Click the P_ALT calculation and verify a footnote appears with the formula.

[jwildfire]

Demo page here: https://bl.ocks.org/jwildfire/e6ac55558cd71f8bd5e46ba35cf6e991

[dschwentker]

Tested and confirmed new filter appears and functions as expected, PALT calculation appears in participant details section when clicking a point that is above the three times the upper limit of normal, and clicking on PALT causes a footnote to appear.