Replace pdftk by pdfunite. 'pdftk' is outdated. It's hard to install on Ubuntu 18. It fails for recent PDFs. 'pdfunite' is based on poppler. URLs are preserved. Orientation and size are preserved.

Download Excel (and all other download types): Content-Disposition header delivered/suppressed in the opposite meaning as it should be. Seems to be fixed now.

Bug 7539: Copy to clipboard not reliable. This commit fixes problems with 'copy file content' to clipboard. Refs #7539

Fixes #3992 (Feature): dbNameQfq & dbNameData already implemented. dbNameT3 renamed from T3_DB_NAME. No more configuration in config.qfq.php necessary. Manual updated.
AbstractException.php: fixes access to uninitialized array elements.
Download.php: get dbT3 now from STORE_SYSTEM
Config.php: read 'dbNameT3' from TYPO3_CONF_VARS or from T3 config file.
QuickFormQuery.php: refactor gathering 'dbNames' - now from config.qfq.php. Fixes bug in getForwardMode() for QFQ inline editing.

F4901: implement split with 'convert' (jpeg). Refactor chmod(), unlink(), rename(), rmdir(), copy() to use by QFQ version which throws an exception.

B6929 - Treat single file argument like several file argument (savePdf: copy, not move) - refs #6929, closes #6929

Download/Excel: Add special column name '_XLSb' and Excel column type 'b' (Base64 encode). Newline in text is correct handled with this option.