Adding more office MIME types to office_converter.

- Without those types the graphics backend will throw 'Unkwon file format' on OCR.
- S.a.
  http://stackoverflow.com/questions/4212861/what-is-a-correct-mime-type-for-docx-pptx-etc

Error:
UnknownFileFormat: File "/srv/mayan/projects/mayan10/mayan/mayan/apps/ocr/tasks.py", line 40, in task_process_queue_document do_document_ocr(queue_document) File "/srv/mayan/projects/mayan10/mayan/mayan/apps/ocr/api.py", line 47, in do_document_ocr document_filepath = document_page.document.get_image_cache_name(page=document_page.page_number, version=document_page.document_version.pk) File "/srv/mayan/projects/mayan10/mayan/mayan/apps/documents/models.py", line 128, in get_image_cache_name return convert(document_file, output_filepath=cache_file_path, page=page, transformations=transformations, mimetype=self.file_mimetype) File "/srv/mayan/projects/mayan10/mayan/mayan/apps/converter/api.py", line 95, in convert backend.convert_file(input_filepath=input_filepath, output_filepath=output_filepath, transformations=transformations, page=page, file_format=file_format, mimetype=mimetype) File "/srv/mayan/projects/mayan10/mayan/mayan/apps/converter/backends/graphicsmagick.py", line 81, in convert_file raise UnknownFileFormat