Division.approver

[florianm]

Problem

Will Divisional Directors want to be the direct SDIS contact and get all emails personally, or would at least one of them nominate a stand-in who will execute all SDIS interactions on their behalf?

Feature

• Add Division.approver (model, admin, serializer, tests)
• Change Project.approvers from project.program.division.director to .approver
• Directors can still be their own correspondents or nominate anyone else (e.g. their A/Dir or their EA)