Cleanups for the invite user flow

[epugh]

Description

This fixes the admin user detail page which assumed that users had agreed to T&C, but that might not apply for invited users who haven't joined.

This also makes the logic aorund pending_invite in the front end better.

Motivation and Context

Now that we have the ability to invite someone, we're finding some places where assumpitons we made don't apply.

How Has This Been Tested?

manually and tests

Screenshots or GIFs (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves existing functionality)
• [] New feature (non-breaking change which adds new functionality)
• [] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [] My code follows the code style of this project.
• [] My change requires a change to the documentation.
• [] I have updated the documentation accordingly.
• [] I have read the CONTRIBUTING document.
• [] I have added tests to cover my changes.
• [] All new and existing tests passed.