new proc "ad_log_deprecated": unified interface for logging deprecated usages
The existing code used a larger variety of different messages to denote invocations of deprecated procs and other artifacts. "ad_log_deprecated" provides a unified interface, and provides a usage hint what to use instead based on the API-doc definitions in the log-file.
- added parameters "label", "disposition" and "file_name_prefix" for better configurability
- added support for updating the current page with feedback of the dropped files. This is used e.g. by the online exam in the exam protocol to display incrementally thumbnails of feedback files.
- change property "uploader" to "disposition", since "uploader" is somewhat ambiguous. "Disposition" defines, what happens after the file was uploaded, e.g. whether the content has to be transformed, etc.