Add sample CI build with notification script

This CI build script is invoked by GitLab CI on each build run and meant to be project specific. The script will run common build tasks (bundle install, rake db:setup and rake rspec) upon each invocation, but you may easily modify the build() function to add your own steps. When the build fails, and email is sent to configured recipients. Instructions are inside the script.

This is a stab to address requests similar to issue #222