TYPO3 6.1+ compatibility

This set of changes fixed the TYPO3 6.1+ compatibility for EXT:dialog.

Dialog now works with current Flux (Master from Git, not TER version), current EXT:vhs and the updated versions of EXT:fluidwidget and EXT:notify I pushed to Github (see pull requests).

The only thing that doesn't work (but also didn't work in the old 4.7 version) is the validation result of DiscussionController->postAction. Instead of writing a meaningful error message, it states: "An error occurred while trying to call Tx_Dialog_Controller_DiscussionController->postAction()".