As a lifter, I want to be able to choose an exercise type, so that Ironlog can plan my workout.

[bstauff]

To provide users with a workout flow experience, we need to differentiate the tasks in a workout.

We will have four types of exercise:

1. Warmup
2. Main
3. Supplemental
4. Assistance

Users will move through stages that contain each type of workout:

Warmup -> Main -> Supplemental -> Assistance

When a user creates an exercise for a workout, they need to be able to indicate what type of exercise it is, using the list above.