Function searches through all 'cpas' and find the 'cpa' which has the smallest amount of clients.
During the client's registration he automaticly find his 'cpa'.
File 'cpa_sessions_controller'.
During creation of document it assigns 'by', 'size' and 'cpa_id' automaticly.
Model cpa session.
File of model 'document' now can be downloaded.
View for client with 'cpa name'.
View for log in 'cpa'.
View to show cpa.
View for document's index with possibilty download new document.
View to show document with displaying thumbnail of it.
Routes file with routes to sign in and sign out cpa.