Create track 4.1 2

The added files are :
/tutor/app/assets/javascripts/tracks.js.coffee
/tutor/app/controllers/tracks_controller.rb
/tutor/app/views/tracks/show.html.erb

The modified files are:
/tutor/models/track.rb (added validations)
/tutor/config/routes.rb (added tracks routes)

Please review me: Issue #179
@rami-khalil @mimikian @Sharaf93 @fadel1493 @mohamedsaeed93