MBS-5719: Track number sometimes missing in rel editor

If a relationship whose target is a recording that's also part of the
tracklist is parsed before the recording node for the actual tracklist
is parsed, then the recording Entity will be missing its number
attribute, among other things.
MBS-5727: Disc [medium] title missing from edit relationships page
Merge remote-tracking branch 'bitmap/mbs-5719' into beta

* bitmap/mbs-5719:
  MBS-5719: Track number sometimes missing in rel editor
Merge branch 'beta' of ssh://git.musicbrainz.org:10015/musicbrainz-server into beta

* 'beta' of ssh://git.musicbrainz.org:10015/musicbrainz-server:
  Update .pot file.
  Clarify why seed-love-bug still exists even though the selenium tests which previously used it have been removed.
  MBS-1774: update tests
  MBS-1774: add type-id attribute and key to webservice results for relations
  MBS-5757: reduce open time for all edits to 7 days
  MBS-5742: clean up chained subtraction/addition, and last_item setting
  MBS-5617: tweak styling to remove explicit linebreaks, since I don't want to argue further
  MBS-5742: use form.field.value.size instead of an explicit counter
  Remove selenium tests.
  MBS-5742: require JS on ISWCs/IPIs only for interactive use
  MBS-5617: remove newimagegoeshere-125.png, replace with div/p and a translatable string