Add Tracking for Body Fat Percentage

[KaladinRand]

Add ability to track body fat percentage alongside weight. Data could interact to show fat mass and lean mass trends.

Seeing my fat mass continue to drop while gaining muscle weight is really helpful in keeping me motivated even when the scale isn't moving much.

Thanks!

[Semperverus]

The calculations for this can be found here: https://www.calculator.net/body-fat-calculator.html