Changing member permissions displays all users on member dropdown

[lauren-johnston]

Describe the bug Changing member permissions displays all users on the org pages. This is not necessarily a huge problem because sites like github show all accounts. However, it feels weird to see them in a dropdown where everything is very visible.

To Reproduce Steps to reproduce the behavior:

1. Go to dashboard
2. Click on an org (if you don't have one, make one first)
3. Scroll down to manage membership
4. Click on manage -> add/change user permissions
5. See dropdown

Expected behavior Invites users by email but does not reveal all users on site.

Screenshots

[lauren-johnston]

This may be helpful (integrates with django allauth) https://github.com/bee-keeper/django-invitations

[lauren-johnston]

Actually it might be simpler than that: https://sendgrid.com/docs/for-developers/sending-email/django/