Enhancement: Alert if try to delete a pkginfo if still enabled in a manifest or catalog

[diwanicki]

If a pkginfo is enabled in a catalog or manifest, alert the user if they attempt to delete it. Notify as to which catalog/manifest(s) it is still active in and offer to remove from those as well, just delete the pkinfo (leaving references to it intact), or cancel.

[hjuutilainen]

Yes, this needs some work. Currently MunkiAdmin only removes references from manifests (and other package infos) if the package being deleted is the last one in the repo. If there's any other packages with the same name key, only the package and installer item is removed.