Users can accept terms and sign permit online

This pull request adds a new step that allows users to sign their permit digitally and accept appropriate terms for the project. This information is then written to the generated PDF, cutting out the process of them printing and signing it.

(Users can now print a final, signed PDF. In the future, we may be able to have them email the PDF instead of bringing it in.)

- [ ] Make a new view for confirm_terms
- [ ] Add new field to the database and migrate
- [ ] Add new step to Wicked controller
- [ ] Write controller logic to validate checkbox and name
- [ ] Make PDFtk generate signature