Part of speech in the learner's language

The part of speech is written in the learner's language.

Changed

• Class is localised. wiktextract normalises the part of speech to an
  English tag whichever Wiktionary edition an index was built from, so a
  German card read noun and a French one read adj. Cards now read
  Substantiv and adjectif.

  The label follows the definition, so it never disagrees with the text
  beside it: with --def-lang fr a German word reads nom, and without it
  the same word reads Substantiv. Constraint 3.3 already allowed Class
  to change language, and this is the reason it does.

  Labels for de, fr, ru, es, it, pt and en are in language.POS_LABELS.
  A language with no table falls back to English, which still expands adj
  into adjective, and a tag with no entry is shown unchanged rather than
  dropped. Adding a language is one row.

• Existing cards keep whatever they were imported with. Re-import to update
  them; nothing needs migrating and no review history is affected.