Basic importer/mapping for consolidated independent data

This imports/maps basic recording and release info from the CI dumps.

There looks to be lots of potential AR data in the dumps (I saw composers, lyricists, producers, mixers, and publishers at least), but didn't find a way to store it using the current json schema, and left it out for now.

There's also genre info and publishing dates on the recordings which aren't used.

Something I was unsure about was the way the XML defines tracklists. Basically, a list of SoundRecordings is defined separate from any release data, and each Release node includes a list of ids/references to the sound recording data. I don't think there's any real "track" info, so the only track data I mapped was the recording field. I didn't know if it was correct to also duplicate the recording name/length/etc. into the track fields, so I didn't.

As far as importing goes, I looked at bringing back the submit-dir.py thing that got removed. The problem I had there is that I needed a way to say "process this entire directory using this specific import manager command" (no luck there...I was thinking I could grab the appropriate command from `import_manager._commands` but was unable to import it).

Anyway, right now the path traversal is builtin to the `ci` command.
So the usual catch with the xml-to-json transform, is: what happens here when there's only one track on a release? Generally it would then not produce a list, but rather just a key, so this might fail nastily.