Add field for providing a description per visibility group

Problem/Motivation

From an architectural perspective it would be useful to have a text field on each visibility group for documenting the purpose behind the visibility group.

Proposed resolution

Add a textarea field on each visibility group for documenting it.

Remaining tasks

Add the field.
Add test coverage.

User interface changes

A new textarea field would be present on each visibility group that would serve as a description.

API changes

TBD

Data model changes

TBD