Long-awaited compatibility version for TYPO3 v12.

Support for TYPO3 v11 is maintained, as usual, but TYPO3 v9 and v10 are not supported anymore.

 We took the opportunity to kickstart support for TYPO3 v13. Right now the extension configuration module does not let you choose the domains to enable. Please copy over settings from TYPO3 v11 or v12 or configure manually.