Merge pull request #85 from tiger-swallowtails-2014/bootstrap_validations

Bootstrap validations
Add Chart.js to asset pipeline
Merge pull request #86 from tiger-swallowtails-2014/spike_charts

Add Chart.js to asset pipeline
Install bootstrap-slider
Add difficulty slider partial
Create difficulty slider widget
Link difficulty slider widget into widget chain
Add CSS center class
Update speed_test route to send back paragraph of given difficulty
Update sample paragaphs with difficulty level
Update speed test spec for difficulty slider
Merge pull request #88 from tiger-swallowtails-2014/difficulty_slider

Difficulty slider
link to buy book with author and title
allow previously searched books to be added to database