Implement CSP hard constraints

[NolanVH]

User Story

As a developer of the CSP implementation I would like to be able to have a set of functions which represent the hard scheduling constraints that I can use to reduce the possible valid assignments of values to variables.

Acceptance Criteria

• [x] All hard constraints from the SRS are implemented using the Constraint class
• [x] Constraint implementations are easy to understand
• [x] Every hard constraint has at least one unit test
• [x] Constraints are carefully analyzed and tested for runtime complexity, and any bottleneck constraints are identified

Related issues

Blocks #15

Additional Resources

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[strdavis]

• Kiana and I integrated the hard constraints with the CSP solver via pair programming.
• All hard constraints are implemented other than the timeslot overlap constraint.
  • Nolan suggested that for this constraint we create a graph of conflicts between timeslots during pre-processing, then reference it during the search to efficiently detect conflicts. This will take some time to implement, so we'd like to do it at the start of next sprint.

[sfaigan]

Carried over to sprint 3 because PR is still open