Allow editing of group description from the group overview page

Problem

Groups can have descriptions, but the description is managed out of an area in the settings. There are two problems with that:

• Users are not asked to add a description during the creation of a new subgroup. That means they might not even be aware that it is possible to add a description unless they stumble across it in settings. This problem is tackled in this issue: Add a group description during group creation (#370468)
• When a user wants to change the description, they have to know that they have to go into settings first, find the appropriate section and then change the description there.

Current group overview page with description:

Current general settings page where the description can be added:

Proposal

Make changing the group description actionable where it appears: in the group overview screen. It could be as simple as indicating that the description field is editable upon hover, or by adding an edit icon.

• Only group owners or maintainers should be able to change the description.
• Users who are not owners or maintainers should not be able to see the interaction to change the description. As they have no access to settings, this is irrelevant to them.
• The ability to change a group description should be removed from the General settings page.
• For groups that do not yet have a description, there needs to be an action on the group overview page to add a description if desired. This action would only be available to group owners or maintainers.