Jenkins should ask for confirmation before aborting a build

Jenkins does not ask for confirmation before aborting a build. Since this can cause significant harm in the case of long-running builds or builds with side effects (partial deployments etc.), this should be added to the abort functionality.

Queued items can be parameterized or triggered in a way that makes them difficult to reproduce (actions added etc.) so those should probably be protected from accidentally canceling them as well.