[!!!][FEATURE] Make BE favicon configurable via Extension manager

Make the path to the favicon configurable in the Extension Manager instead
of the TBE_STYLES.

Releases: master
Resolves: #77481
Change-Id: I6162b031b13077ea9c06d54754f58e09f6a1bce5
Reviewed-on: https://review.typo3.org/49202


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>