Cannot remove stereotype

[Geert Bellekens]

If a user doesn't have the "Configure Stereotypes" right he cannot remove a stereotype from an element.

Steps to reproduce:
- Log in with a user without "Configure Stereotypes" rights
- Create a new element and choose a stereotype
- Save element
- Open element again and try to remove the steotype
   - You can't remove it using the dropdown since there's no <none> selection available
  - You can't remove it using the [...] button by unchecking the stereotype since that doesn't seem to have any effect.

Reported to Sparx

Geert