Sync since last activity feature

[fowie]

Hey all,
Love the software. I created a feature that grabs the latest activity from Garmin, and then uses that timestamp to figure out which workouts to retrieve from Peloton, and uploads all workouts newer than the latest activity. This way you don't have to know how many activities to upload, you just set [Peloton][GetLatestWorkouts] = true and you can leave the program running indefinitely. I'd love to see it incorporated back in, but I'm not sure how to get a branch so I can push it up for others to test?

[fowie]

Nevermind, started a fork and I'll put in a pull request once I've finished implementing tests.