Add camp roles to officers

[spookylukey]

Requirements

• Officers added to a camp list should be given a role
• When reference is being taken, roles for relevant camps should be displayed to the referee
• Roles should include:
  • Leader
  • Assistant leader
  • Chaplain
  • Tent Officer
  • Junior Tent Officer
  • Lead Kitchen
  • Kitchen Helper
  • Site maintenance

Implementation

• New CampRole model with name field
• Invitation gets camp_role field. Must be nullable because of old data
• Probably need to completely rework the leaders' camp officer list page to get this info to be added as part of the process.
• Add the role information to the reference collection form

[spookylukey]

This was implemented in 4a697843d9b4b4b132d7c3326e146064f3be93d3 and earlier commits.