Add user site credits to member edit page

[MaximilianoRicoTabo]

ENHACEMENT: Add Site Credit panel for v3.1 compat sake

All Submissions:

• [x] Have you followed the Contributing guidelines?
• [x] Does your code follow the WordPress' coding standards?
• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changelog entry

Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.