Create data access interface for Case

[tylerthome]

Overview

Create access methods for Case entity against MongoDB to enable our system to model case creation and updates

Action Items

• [x] Define method: create_case(case_worker_id, guest_id)
• [x] Define method: update_case_status(case_id, status_id)
• [x] Define method: reassign_case(case_id, case_worker_id)