This should close #95.

without /etc/ld.so.cache available in the sandbox, tests fail on gentoo with:
/usr/bin/ffmpeg: error while loading shared libraries: libstdc++.so.6:
    cannot open shared object file: No such file or directory

This should make easier to get more metadata from
archive-based file formats.

intrigeri authored 6 years ago and jvoisin committed 6 years ago

This should closes  #90

- This commit introduces optional dependencies (namely ffmpeg):
  mat2 will spit a warning when trying to process an .avi file
  if ffmpeg isn't installed.
- Since metadata are obtained via exiftool, this commit
  also refactors a bit our exfitool wrapper.

Since FLAC files can contain covers, it makes sense
to parse their metadata

Relates 0a2a398c

We didn't take the whitelist into account while
removing dangling files from [Content_types].xml

- Replace some class members by instance members
- Don't thread the cleaning process anymore for now