Added the rest of entities. Added exception file for courseNotFound exception. Modified the interface for adding a course. Added the code for adding a course. 

Could not test the addCourse method -> needs revision (might be buggy)

Commited again because git does not recognize my username

Programmer : Raul
Added the rest of entities. Added exception file for courseNotFound exception. Modified the interface for adding a course. Added the code for adding a course. 

Could not test the addCourse method -> needs revision (might be buggy)

Commited again because git does not recognize my username

Programmer : Raul
Added the rest of entities. Added exception file for courseNotFound exception. Modified the interface for adding a course. Added the code for adding a course. 

Could not test the addCourse method -> needs revision (might be buggy)

Commited again because git does not recognize my username

Programmer : Raul