Treat paths as binary blobs, not unicode strings

Since paths can contain any arbitrary characters, and are essentially
treated on-disk as binary, Archivematica needs to treat these as
binary strings that could contain any arbitrary characters.

This alters several database fields to be binary types, alters several
bits of intenral code so that paths are always treated as str types
instead of unicode strings, and fixes up a few existing bits of string
decoding to ensure they can cope with non-unicode strings (at the cost
of potentially creating mojibake).

refs #6067
clamscan script: adjust string escaping