Create initial Models for competencies

[AdrianDAlessandro]

Is your feature request related to a problem? Please describe.
We need to be able to populate the database with the competencies and skills that form the framework.

Describe the solution you'd like
Currently the framework has three tiers. So I suggest we make three models, one for each tier: Models to match the schema in the Below comment:

• Create Category Model #82
• Create Skill Model #83
• Create UserSkill Model #84
• Create SkillLevel Model #85

Additional context
We need to determine a sensible database schema for the competencies, the above suggestion may serve as a "good enough" first step, but someone with experience designing database schemas should have a proper think about this.

[AdrianDAlessandro]

Updated Schema Diagram