Update from Bootsrap 2.3 to 3.2

 - Change grid classes from .spanX to .col-md-X
 - Change navbar markup to match new components patterns
 - Change vars and mixins in imperilment.css.scss
 - Update simple_form and use it's bootstrap option
 - Change form groups and controls to new classes (many forms are unused anways)
 - Remove Bootstrap classes from <select>s manually in application.js

Change-Id: If8cdf848e920636fa4119c9ec210d10da801aaee