Adding Javascript runtime to MarkUs
Warn user if bundler version is to low

As we are enabling the support for ruby 2.0 platform (mri_20 in
Gemfile), we need to have Bundler >= 1.3.5
Merge pull request #1336 from benjaminvialle/execjs

Adding Javascript runtime to MarkUs
Merge pull request #1386 from benjaminvialle/bundler

Warn user if bundler version is to low
Merge branch 'master' of github.com:MarkUsProject/Markus