[+FEATURE] TYPO3: We now have a somewhat better setup controller which allows to import content and create admin users, resolves #8284, resolves #8285.
[~TASK] TYPO3 (Domain): Removed early return from hasChildNodes() in AbstractNode.
[~TASK] TYPO3 (Domain): addChildNode() and getChildNodes() on Site only handle the 'default' section now.
[-TASK] TYPO3 (Domain): getIndexNode() no longer expects a section parameter and returns NULL if no node was found.
[+TASK] PhoenixDemoTypo3Org: Added Sites.xml with the test content.
[+TASK] FLOW3 (Package): added isPackageActive() to the PackageManagerInterface.