change "affiliated user" to "member"

[wholmgren]

The Administration and Data Sharing documentation struggles to convey the concept of an "affiliated user" - a user that belongs to an organization but doesn't have full access to everything by default. We should copy Github's approach and use the term "member" to describe these users. Screen shot of Github's role management interface below:

I don't feel like owner is that much more clear than admin for SFA.