AutoCron: Added doc for autocron. Extend AutoCron.php to be MultiDB aware. Update der AutoCron form.

Feature 4720 / Separate Database for Form & FormElement - Multi DB - fixed problem that 'Quick Edit Form / FormElement' has been broken in MultiDB Setup.

Feature #5571 / File Upload: save filesize and mimetype automatically in 'upload mode simple',if those columns exist.

- STORE_VARS contains now 'mimeType' and 'fileSize'.
- sqlBefore and sqlAfter will be fired in Upload Advanced and new in Upload Simple as well.
- STORE_VARS contains now `filenameOnly`. It can be used in downloadButton=....

# Conflicts:
#	extension/qfq/qfq/database/DatabaseUpdateData.php

Bug: Form: 'FormElement' > 'Container' - relied on '{{formId:S}}' even if the FE record already exist - fixed

Feature 5425 / thumbnail: rewrite - secure thumbnails are now rendered on first access, not when 'AS _thumbnail' is called.