Added gitignore for TYPO3 CMS version >= 6

As the TYPO3 CMS had a major file-refactoring in version 6.0, here is an updated .gitignore file.

Here's a breath summary of things that changed on the file-level:
* Added /fileadmin/_processed_/ for processed image-files like thumbnails
* Added /typo3conf/AdditionalConfiguration.php instead of the file localconf_local.php that was just a _best practice_

In this .gitignore I also added all files that exist in the dummy-package. These are f.e. to keep directories that the system itself does not create if they're gone.