[TASK] Improve page tree in access module

If the root page is selected, the following is improved:

- show the sitename instead of '[root-level]'
- show the world icon for the first pages (all with pid = 0)

Resolves: #79857
Releases: master
Change-Id: I449a34e356ec43f8679bb9cdcd4c790fd4701004
Reviewed-on: https://review.typo3.org/51719


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Thomas Hohn <thomas@hohn.dk>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>