[FEATURE] Refactoring multi view

[markusweigelt]

• Refactored multiview functionality based on iFrames
• Refactoring most DFG-Viewer resources to tx_dlf_multiview plugin for reusabiliy
• Removed unnecessary implementations related to the legacy multiview
• Fixed known bugs related to the legacy multiview
• Added a document button: In the single view, document types configured as multiDocumentTypes as setting for multiview plugin will redirect directly to the multiview (improved configurable behavior of legacy multiview).
  • When added documents are removed from the multiview, and the initial document belongs to a single view, the user will be redirected back to the single view
• Improve loading behavior
• Navigation improvements