Add q uniqueness validation to eval template

- Add question uniqueness validation to EvaluationSurvey model (to
  prevent duplicating questions)

- Also, put deadline notifications in alert divs
Add GitHub link to footer

- Also, begin implementing option to make evaluation template questions
  mandatory
Finish mandatory / optional feature for eval q's

- Finish letting admins set evaluation template questions as either
  mandatory or optional

- Finish validating that mandatory questions are responded to when
  creating an evaluation