Printing

This implements support for printing through CMS. I've added a PrintingService (PS) accepting print jobs through the database from CWS. PS accepts PDF and text files. The latter are converted to PDF using the a2ps command line utility (which does syntax highlighting). It then adds a title page that is generated by pdflatex. Finally, the result is sent to the printer. You can enforce a file size limit of the submitted file, a maximum number of pages (text files are stripped off all pages above this limit, too long PDF files are rejected), and a maximum number of submitted print jobs. You can disable printing PDF files if you want.
I guess I called it a length because there are already ``max_submission_length`` and ``max_input_length``. But size would indeed make more sense.