With displaying the count of failed error checks in the navigation menu
(like the count of unread messages in an email inbox) a user will more
likely enter the "System environment" section of the install tool and
take care about the found errors and warnings.

Change-Id: I3d9b628b428da13992c3dc1e7e5ab6beaeda5ce1
Resolves: #51410
Releases: 6.2
Reviewed-on: https://review.typo3.org/23380
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters