Feature request: allow instructor to upload pdf/image to student endorsements.

[JPSloan1]

Potentially two separate stories: As an instructor, I can view the uploaded image/pdf endorsements for a student who has given me permissions As an instructor, I can upload image/pdf endorsements for a student who has given me permissions

[ericberman]

Student can control this:

• "Can view my logbook" grants/revokes permission to see endorsements issued by other instructors and any scans that were uploaded
• "Can add flights to my logbook" grants/revokes permission to upload additional scans. (You always have the ability to add a digital endorsement.)