Supervisor can edit their display name

[Zrrrpy]

Part of epic #105

What type of user is this for? [admin/supervisor/volunteer]
supervisor

Where does/should this occur?
In the supervisor dashboard (doesn't exist yet, but is ready to) on a page equivalent to this one for admins (except email should be static).

Description
Supervisors should be able to edit their display name (but not their email. Additional info on supervisor role permissions can be found in issue: #30

Screenshots
(except email should be static)

Relates to issues:
#30