Organizations

## Is your feature request related to a problem? Please describe.
Like Github organizations, I'd like to assign each user to an org, and when that user searches for other users to add to spaces, his autocomplete queries are scoped to the org he is in such that he cannot see every user on the system and privacy is preserved.

## Describe the solution you'd like
I want to have multiple non-profits on the same instance and not worry about them seeing each other when doing searches or assignments.

## Describe alternatives you've considered
Hacking the code to filter based on email URL/ domain.

## Additional context
Add any other context or screenshots about the feature request here.