www/rubygem-rails5: Create new port for version 5 of Ruby on Rails

Along with the new rails version 5 port, some rails5 dependencies had to be
created to avoid conflicts.

New ports added:

devel/rubygem-coffee-rails-rails5,
textproc/rubygem-sass-rails-rails5
www/rubygem-jquery-rails-rails5
www/rubygem-rails5
www/rubygem-turbolinks-rails5

Reviewed by: mat
Approved by: swills (mentor, implicit)