Allow configuring transformations to be applied to the filename before

parsing. The motivation was that files produced by a Brother scanner
wouldn't match paperless' expectations. At most one transformation
is applied (first matching). It won't affect the filename on disk.

This is generic enough so that it is useful for various purposes.
In my case it allows me to use the different hardware buttons on
the scanner to use different profiles, feeding one instance of
paperless with documents of multiple entities and tagging them
accordingly.

Example:

PAPERLESS_FILENAME_PARSE_TRANSFORMS=[{"pattern":"^([a-z]+)_(\\d{8})_(\\d{6})_([0-9]+)\\.", "repl":"\\2\\3Z - \\4 - \\1."},{"pattern":"^([a-z]+)_([0-9]+)\\.", "repl":" - \\2 - \\1."}]

src/documents/models.py

@@ -483,8 +483,14 @@ class FileInfo:
           "<title>.<suffix>"
         """
 
+        filename = os.path.basename(path)
+        for (pattern, repl) in settings.FILENAME_PARSE_TRANSFORMS:
+            (filename, count) = pattern.subn(repl, filename)
+            if count:
+                break
+
         for regex in cls.REGEXES.values():
-            m = regex.match(os.path.basename(path))
+            m = regex.match(filename)
             if m:
                 properties = m.groupdict()
                 cls._mangle_property(properties, "created")