Update ReST Syntax URLs. Remove 'extension/Documentation.outdated'. Update .gitignore to not commit rendered doc.

F4922 / Excel Import: remove PHPExcel, new PhpSpreadsheet. The lib is not part of QFQ Repo - to install locally, do: make Bootstrap

Manual.rst - Doku angepasst
Download.php - Mime type wird nicht mehr an Dateiname angehängt

Implemented: file upload check for mime type and max file size.
File.php, AbstractBuildForm.php: Implement FE_FILE_MIME_TYPE_ACCEPT and FE_FILE_MAX_FILE_SIZE

.gitignore: added qfq*.zip to ignore. The '*' is important in case the extension are generated with the version number included in the filename.

Changed Makefile: please do

  rm -f .bowerpackages .doc_plantuml .npmpackages \
   .phpdocinstall .plantuml .support .support_plantuml
  rm -rf doc
  make bootstrap

QfqForm.js: support `required` configuration attribute.