Last of the media improvements (Issue #5167)

Last of the media improvements (Issue #5167)

cups/dest-localization.c:
- Use "other tray" and "other media" for unknown media sources and types.

cups/dest-options.c:
- media-key is king for size matching.
- Synthesize a media-key value using the size name unless we can't get one.

cups/language-private.h:
- Add _CUPS_MESSAGE_PO constant.

cups/pwg-media.c:
- Allow PWG names with a trailing "_foo" qualifier (so media-key still works
  if an application just adds the _cups_size_t.media value as the "media"
  option.

locale/*.{po,pot,strings}:
- Update localization strings.

locale/cups.footer:
- Add common HP and Canon media types.

locale/checkpo.c:
- Fix \ validation.