Validate new Learners and Instructors

Validating single entries on the Instructor and Learner tabs - with tests
Validating CSV uploads and displaying errors by line for these tabs - no tests, couldn't get the file upload to work correctly.


Need to confirm that these messages are correct:
- [x] Last Name is Required
- [x] First Name is Required
- [x] Email is Required
- [x] Campus ID is Required
- [x] Email address is not valid
- [x] Campus ID is not long enough
- [x] Campus ID is too long
- [x] Incorrect Number of Fields
- [x] A user with this email is already in the system
- [x] Email address in the file more than once

Fixes #561