Show Warning on Closing a Ticket without Action

[freinhard]

Show a warning to the user if a ticket is about to be closed with an excepted action such as:

• Accepting a reservation
• Accepting an publishing an event
• etc.

[href]

Implemented in https://github.com/OneGov/onegov.org/commit/b9e6de587e6b77f0bee0c8242cd37c3bfcc6ac68