Add pry to gemfile
Add Exercises model and migration
Add source_url to Exercises table
Add category to Exercises and create seed data
Add Workout and Workout_Exercises migrations
Add "has many" relationships...

...to workout and exercise models
Add exercises controller and basic search form
Add exercises list to exercise index
User can generate randomized wokout with...

...a given duration (in minutes) and category
User can log in

- Add gem 'devise' to Gemfile
- Install devise and add devise User model
- Add flash messages to layout
Remove login field from Users migration
Set default name on Workouts
Add Users to seed data
Add User reference to workouts table
Add devise
User can save workouts
Redirect save to workouts index rather than back