Modularize front-end
In order to enable Blacklight to support multiple different front ends move
views to blacklight-bootstrap2. Eventually we'll add
blacklight-bootstrap3.

In order to run blacklight with the boostrap 2 front end you can remove
`gem 'blacklight'` from your gemfile and replace it with `gem
'blacklight-bootstrap2'`.  If you continue to use `gem 'blacklight'` you
will get the bootstrap2 front end by default.
Moved view tests into blacklight-bootstrap2
Move stylesheets to blacklight-bootstrap2
Added build for bootstrap 3 and bootstrap 2
Pair down the number of travis builds temporarily
Convert spanX to col-md-X
Convert form controls to bootstrap 3
Separate out assets and generator for bootstrap 2 and 3
Give the header a non-transparent background
Pad the user-util links for bootstrap3
Fixed modals for bootstrap 3
Merge pull request #639 into both front ends