Release 3.0.0

RELEASE Major version 3.0.0 release
FEATURE Compatibility with TYPO3 v11.5.x
FEATURE Improve backend usability with TYPO3 backend preview
FEATURE Re-import/export page tree
BUGFIX UI/UX small design issues fixing
BUGFIX Functional testing and bug fixing
TASK Drop the dependencies of EXT.gridelements
TASK Drop the support of TYPO3 v9.x
TASK Code cleanup and code improvements