HTML mock-up of new design.
Start converting HTML mockup to React.
Say "See another" instead of "Do another" for yellow exercises.
Converting mockup to React ExerciseComponent
Implemented blue lessons and showing real output.
Added link to Basic Ruby logo.
Add line numbers to error messages.
Add no-repeat so resizing pages doesn't add ugly repetitions.
Merged in earlier changes (repetitions feature, additional lessons,
print method).  Merge branch 'master' into simplified

Conflicts:
	app/views/main/exercise.haml
	db/curriculum.yaml
Removed comment lesson; removed assignments; added some starting code for the variable lesson.
Improve banner so it's clear what you're asked to do.
Wrote some blue lessons.  Putting solutions under cases instead of solution, because there are multiple solutions when there are multiple cases.
Expanded actual and expected boxes to be able to show multiple cases at once.
Oops, left title hard-coded at lesson 1.
Auto-run green programs too, so empty output is visible.
Always show gets programs with multiple inputs.
Remove under-construction icon from blue exercises.
Hide orange exercises instead of showing them under construction.
Rescaled the yellow, blue, and red icons for 60x60 instead of 30x30
"See another" and "Go on" buttons for yellow and blue; "Show solution" button for red and green.