Refactor associations #65
Description
Model associations are just represented by strings (then extracted for SQL statements) rather than having actual associations and appropriate lookup tables. This causes problems, for example, in Videos and Concepts many-to-many relationship that is just stored as a string of an array of id's ([5, 11]) and Concept.find_by(id: @videoData[0].concepts) doesn't find the associated concepts because it is searching for a singular id "[5, 11]"