SYSTM FIT Export per Jessica Hamilton

Adds a download button on SYSTM workout pages for creating a FIT file for use on your head unit. Use the indoor/outdoor buttons to select which variation to download. Clicking on the blue Wahoo X icon in your extension menu will also allow you to toggle on/off adding open targets at the beginning and end of the workout, as well as displaying your current 4DP metrics.

You can also choose the target power range to either be target + 10%, or fixed zones, based roughly on what's described at https://support.wahoofitness.com/hc/en-us/articles/7671514838674-Wahoo-SYSTM-Outdoor-Structured-Workouts.