Add next workout and previous workout links on top of Workout Edit page

When editing a workout, it would also be convenient to have a “next workout” and/or “previous workout” link on that page, so that after saving changes, I could just go directly to the next workout in the list without going back to load the whole list of workouts. Since my Speedcoach workouts are usually broken up into 2 or 3 separate files, I run into this a lot.