Make new eval form preserve fields if invalid

- If an advisor submits an evaluation and it's invalid, we populate the
  form fields with the old data so the advisor doesn't have to enter it
  all again

- Also, specify version or tag numbers for all gems in Gemfile
Add basic "remove" buttons to eval radio btn form

- Clicking one removes the corresponding input field, but does not bump
  down the indices of fields with higher indices