Allow manual entry when a match is not automatically found

[NicholasConrad]

It appears at present that there is no way to allow bragibooks to process mp3 files into an m4b file if it is unable to find a match. This is sub-optimal as I can always add metadata later if an automated match is not found, but it is much more difficult to manually stich mp3s into an m4b.

Users should have an option to manually enter output scheme supported fields. Then process the mp3s into m4b format and move the resulting file to the output path using manually entered values. Alternatively, there might be an alternate path specified in the settings for 'unmatched' files, and bragibooks could proceed with the mp3 to m4b processing using the existing filenames, and place the resultant m4b files into the 'unmatched' path for manual post-processing.