PDF/fileSplit: uploaded PDF file with missing extension '.pdf' have not been recognized as PDF files - fixed.

splitPdf: using 'fileSplit=jpeg' and uploading a PDF with only one page, results in split.jpg. Now, split.jpg is renamed internally to split-0.jpg to provide a repair shell script a unified naming scheme.

Fixes #7925. a) change CWD during split reduced to splitting only. b) fixed problem in mkDirParent() with absolute paths, c) make logger independent of CWD, d) fixed problem with `mktemp --tmpdir`(difference Ubuntu 16 / 18) by using PHP function, e) fixed some 'undefined index' problems

Fix problem in upload elements: a) in exception FE_ID was not reported, b) fillStoreVar was not fired.

Logger.php: remove UserAgent - that one is logged in FormSubmitLog Table. Add 'cookie' to filter individual actions.

F4901: implement 'delete split files' if primary file is deleted (record) or exchanged against a new one.

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

Upload: rename 'chmod' to 'chmodFile'. Implement 'chmodDir'. Permissions applied for all new created directories.