Backend: Fix support of documents with unusual names

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Backend: PEP8 compliance

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Backend: remove non-ascii chars

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Frontend: PEP8 compliance

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Merge branch 'testing' into unstable