[TASK] Cap counter of "Application Overview"

The issue counter of the "Application Overview" menu gets capped if
there are more than 99 issues by appending a "+" sign. This solves a
overflow issue if there are too many "unread" issues, that may occur
e.g. after creating a new admin user.

Change-Id: I285f930c79b1d56384affbbae77a196aaaa5b65e
Resolves: #73084
Releases: master, 7.6
Reviewed-on: https://review.typo3.org/46451


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Tested-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>