[TASK] Sort extensions by key

Change-Id: I1efc3cbaaa4473316da29fb6f596f07a2dfc0df1
Resolves: #63140
Reviewed-on: http://review.typo3.org/34467
Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Tested-by: Xavier Perseguers <xavier@typo3.org>