Resolve and simplify People for CrewMembers

Creates a list of `CrewMemberAndPerson`s from the `CrewMember`s on a
piece of `Content` when simplifying by resolving the `CrewMember`s
identifiers to `Person`s.
Merge pull request #315 from atlasapi/mbst-6614-content-people-images

Resolve and simplify People for CrewMembers