Since WordCamps might have Contributor Day and we have fields for that on the WordCamp tracker, we should ask about that also during the application process. Right now the Deputy vetting the application or mentoring WordCamp needs to ask this in order to get the tracker data to reflect the right situation.

This PR adds a question about organising Contributor Day and options to choose at which point of the WordCamp they are planning to have it.

Fixes #276

Screenshots

Screenshot before the field was added.
Screenshot after the field was added.

How to test the changes in this Pull Request:

1. Go to the WordCamp Organiser application page
2. Fill out and submit the application, new field should be visible
3. Check the application on WordCamp tracker, Contributor Day checkbox is checked and original application rows contain the answer