Beets-oldestdate

The project is now available on PyPi and can be installed via pip.

- Fixed issue 5 where dates without a month or day would take precedence over those with them
- The plugin now priorities more specific dates (if available) e.g. 1972-05-18 over just 1972
- When saving, remove month/day information if not present, instead of using the 1st of January
- Changed `overwrite_year` option to `overwrite_date`
- Plugin now saves entire date to file, when available
- Fixed `both` approach not keeping older date from recordings after checking releases
- Filter out covers if current recording is not a cover
- Added thorough automated tests to catch as many bugs as possible

A debug statement had managed to sneak its way into the released code. It has now been neutralised.

* Cut down on API calls by filtering candidate recordings on import
* Weight down no work_id tracks to avoid matching them
* Add workflow to prompt user when no work_id is found
* Includes being able to use just the chosen recording or skip date check
* Show user oldest year found from recording to make informed choice
* Deal with covers properly (only for releases mode)
* Avoid crashes when date can't be parsed
* Add option to use file's embedded date