[BUGFIX] Installing TYPO3 -> Installing TYPO3 CMS

Use correct product name in title tag and box during installation.

Change-Id: I21141aa06c12c1abf7fff83e1e33148be6c6373f
Resolves: #51946
Releases: 6.2
Reviewed-on: https://review.typo3.org/23784
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn