Delete role

[johannsell]

User should have the possibility to delete their role. Consider the implementation of Drops #327. Drops handles the condition that another user has to exist that has the same role. Print a message to the user, if the condition fails.
Additionally, the user has to confirm their decision to delete a role before the deletion is executed.

Employees and admins also have the right to delete anothers user role.

The function will be implemented as a button inside the VcARole component that is labeled using an X. It is only shown if the currently logged in user has the right to delete the role (if the shown user is her- / himself or if the currently logged in user has the role employee or admin).