Remove dead code

* Removes builder calls to non-existent methods
* Remove clearance generator, as clearance isn't in the Gemfile
* Remove unused copy_libraries method
Remove unnecessary deletions of files for Rails 4

* Rails 4 doesn't generate index.html or rails.png
Add pry-rails

Every project I've been on has had *at least* pry, and usually
pry-rails (which just makes pry load for rails console).