Allow admins to add warnings for users

[HenriBeck]

Epic: #260

There should be a button on the profile page of each user where admins can add a warning to the user.

• This button should only be visible for admins and higher roles.
• The button should open a modal
• The modal should have a select where the admin can select a type
• The modal should have a text area where the admin can add a comment
• The modal has a Dismiss button
• The modal has a Add warning button