Rename workout.Workout to workout.WorkoutView
Add underscore.js
Add underscore to requirejs conf
Refactor workout view to use the new 'model' module

Move REST loading into its own 'model' module and refactor the workout
view to use the classes provided by model.  Instead of mixing AJAX
code with rendering HTML, we now do AJAX in model and have it refresh
the view with callbacks.  This separation will make the UI code less
dependent on the particular REST API we use.