Support adding/removing a control's class

[Bronstrom]

Description

As a user of the OSCAL Viewer/Editor, I would like to be able to add/remove the class of a control.

Acceptance Criteria

• A new control class [0 or 1] can be added
• A control class can be removed

Proposed Solution

No response

Additional Notes

No response

Implementation

• I can (or plan to) submit a pull request to implement this
• Implementing this may result in a breaking change