0.1.31

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- Use $XDG_CACHE_HOME/thumbnails as per spec change (bug #10613)
- Move xdt m4 macros into separate directory
- Update xdt m4 macros
- Bump autotools requirements
- Fix IT_PROG_INTLTOOL warning
- Fix all m4 warnings
- Enable support for video/webm in ffmpeg thumbnailer plugin (bug #10360)
- Translation updates: Asturian, Bulgarian, Croatian, French, German,
  Greek, Norwegian Bokmål, Polish, Romanian, Slovak, Spanish