Deduplicate artist credit JSON
MBS-7251: Adding a new artist from the track AC bubble closes it
MBS-7252: Country/work lists not sorting

Adds an appropriate reference to sort_in_forms back to select_options.

Removes a duplicate get_collator function.
s/(Change all artists on this) medium/$1 release/
Change track artists even if Done isn't pressed
Show "appears on" data for existing recordings
Fix data-loss in 2c610293, add to Edit::Release::Edit

In the _edit_hash functions, falling back to '' for undefined comments
happens even if a comment doesn't exist in the edit data. So, if just
an entity name was changed, the comment would be silently cleared
without showing up in the edit diff.

Expand the general behavior here to Edit::Release::Edit, since it was
forgotten in 2c610293.

In the JavaScript, no longer encode empty comments as null. Use empty
strings instead. This avoids all of the above entirely.
Better track parser matching to existing tracks

The current code will loop through all the parsed track data, and then
loop through all the existing tracks to find a match to whatever was
parsed. If the track it matches with was already used, however, it
doesn't check if the match is better than the previous one. The new
code does. Additionally, we now first check if there's a good match to
the current track in the same position. If there is, we use that and
don't perform any further matching.

Some functions and constants related to metadata matching were moved
around as part of this patch.
Revert "Update the track parser text as the user changes the options"

This reverts commit c0fb18a773a2b3cb6569abf690ac3294b221224b.

After discussion, it seems this is more annoying than useful. If you
forget to check an option (say, for track numbers) before parsing,
it'll add those numbers to the track titles, but then if you re-open
the parser dialog and check the option, it'll add duplicate numbers to
the tracks.
Allow pressing enter on AE checkbox to submit
Fix FreeDB import seed
Revert small part of d09a7b2

Don't cease to perform further matching if the track in the current
position already matches. I realized this could be detrimental for
tracks names that are mostly identical but then reordered.
Merge remote-tracking branch 'bitmap/release-editor-gsoc' into beta

* bitmap/release-editor-gsoc:
  Revert small part of d09a7b2
  Fix FreeDB import seed
  Allow pressing enter on AE checkbox to submit
  Revert "Update the track parser text as the user changes the options"
  Better track parser matching to existing tracks
  Fix data-loss in 2c610293, add to Edit::Release::Edit
  Show "appears on" data for existing recordings
  Change track artists even if Done isn't pressed
  s/(Change all artists on this) medium/$1 release/
  MBS-7252: Country/work lists not sorting
  MBS-7251: Adding a new artist from the track AC bubble closes it
  Deduplicate artist credit JSON