Added file upload.
Use Getopt.php in bin/xtm_export.php
File upload: Added "MIME type" occurrence. Topic type is now only "Image object" if the MIME type is "image/*".
bin/topic_id_to_subject.php tool
Added an "Upload a file" link to the page header.
Use XTM 2.1 instead of 2.0 syntax for import/export.