[DONE] Small improvements for Zwift export

[R2Tom]

Intervals.icu and Zwift Integration is live!

Unfortunately the Zwift API does not support the show_avg attribute so I had to leave that out. I have asked if it could be added. The Zwift home screen shows the workout(s) scheduled for today. If I encode the date in the name of the workout it will end up in the name of the completed activity which isn’t good. I have asked Zwift about this. Currently there isn’t an API endpoint to do that.