Open and Edit Permission Schemas

As an Admin I'd like to be able to open existing Permission Schemas and edit them
Acceptance criteria:

• When Admin presses on one of the Permission Schemas with right mouse button, he's able to see an Edit menu item. A window with all the groups inside schema, their properties and permissions should be visible. It's possible to add permissions or change the properties of the groups.
• When use presses right mouse button on the Permission Schema, a Delete menu item should be shown. While pressing it, Admin should be shown a confirmation dialog. After confirming, the selected schema should be removed.
• It should be not possible to remove an Active schema.