gemfile: add autoprefixer-rails, remove redundant modular-scale gem
add autoprefixer to config.rb, remove all vender prefixes with the exclustion of some -webkit- specific ones
gemfile: add gem versions
Merge branch 'feature--autoprefixer'

* feature--autoprefixer:
  gemfile: add gem versions
  add autoprefixer to config.rb, remove all vender prefixes with the exclustion of some -webkit- specific ones
  gemfile: add autoprefixer-rails, remove redundant modular-scale gem