Fixes DS-293: Adds PartnerMember model and PartnerMember-User relationships
DS-293: Partner Members: Using PartnerID set by API header auth filter method; refactors mockApiAuthFilter() to apiAuthFilter()
DS-293: Checks strictly against PartnerID during user lookup, if PartnerID is set
Merge pull request #5 from mshmsh5000/DS-293_PartnerMembers

Fixes DS-293: Adds PartnerMember model and PartnerMember-User relations