Add data loading and modals in user management

[Maximus404]

Summary & Motivation

Adjusted styling in the button component and added modals. Added dataloading for usermanagement.

Checklist

• [x] I have added a Label to the pull-request
• [x] I have added tests, and done manual regression tests
• [x] I have updated the documentation, if necessary

[tjementum]

Exciting 🙂

I’m reviewing and testing, but I get this error when testing. I have not had time to troubleshoot.

It would be great if you could change all commit messages to use the imperative form. E.g., change “Added avatar component” to “Add avatar component.” And then force push. I've updated the pull request tilte to follow the same format.

Also, please make a thorough pull request description describing all the changes. E.g., look at old pull requests for inspiration. With a big change like this, it would likely be several paragraphs.