Create new ModelDao class and move there methods: parseModelJSONFile(), getModelJSONFileContent(), saveModelJSONFile(), convertModelToJSONString().
Change CourseDao constructor.
Rename CourseDao to CourseCRUD and make it singleton.
Added onDestroy() on Player activity and destructor() method on Model class.
Added javadoc to CourseCRUD.
Was rewritten in the functional part of the courses and tracks added to lists.
Added 9-patch shadow to drawers
Added methods equals(), hashCode() and toString() for classes: Track and Course.