UI - settings - allow revisioned editing of comment fields in management and gateway

[tpurschke]

To allow admins to comment on a manual change to a management or gateway:

• Immediate implementation (size S): Allow (fw-)admins to view and edit the comment fields of managements and gateways; use large multi-line fields for these comments
• Backlog (size M): replace simple comment fields with auditable comment log (with automatic addition of admin user id and timestamp for each comment
• build a generic comment management functionality also to be used in request module