Lvuiui 79

@xcomanche, @kuzbida , @mariyamoroz , @MyrosiaPabyrivska, @vdanyliv , @lhalam 
Guys, please review if any updates needed.
I moved all active record classes into a separate file (models.rb), so now you can use multiple DB updates within a single request. For example:
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put '/users/:id' , :provides => :json do
  pass unless request.accept? 'application/json'
  @user = User.find(params[:id]) # find record from users DB table by ID
  @teacher = Student.where(userId: (params[:id]) #find record from students DB table > userID collumn
  @user.make_changes                  # make changes to users table
  @teacher.make_changes             # make changes to students table  
end
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