Support users without a role

[dparker1005]

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Changes proposed in this Pull Request:

WordPress allows users to not have a role. In our Edit Member page, we don't support that option, so we default to the first value. This default could be a "powerful", like Membership Manager. If the page is then saved, the user will actually be given that role.

The fix is to have an option for "no role" and this PR is based on the core WP Edit User code here:
https://github.com/WordPress/wordpress-develop/blob/13fd2f829b01156174d1ca7ca2236eb9c7248e42/src/wp-admin/user-edit.php#L453-L461

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Changelog entry

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