Fix and refactor Start a New Course form

Fix escaping of commas and double-quotes in course names by refactoring code from `CourseFormController`:

1. Isolate code responsible for generating CSV into separate class (`SFU::CourseForm::CSVBuilder`)
2. Use the CSV module to generate CSV (comes with comma and double-quote escaping)
3. Refactor code to simplify and de-clutter
4. Define spec to facilitate testing