Allow users to create roles when creating users

[timoschwarzer]

I often create a new role for each user to have granular control over user permissions. This PR makes this easier by adding an option to create a new role on the fly while creating a new user:

[ssddanbrown]

Thanks @timoschwarzer for providing this and apologies for my late feedback.

While I can definitely see the use-case/benefits for some people at the moment, this is not a feature that I'd specifically want to add. Realistically per-user roles are a workaround for a lack of user-level item permissions which is something I'd still like to attempt later on in the roadmap. Additionally, encouraging users to potentially create one-off roles where not explicitly needed could lead to performance considerations, especially with large user-counts. Therefore I'm going to close this off, Sorry.