Add unachiver support

Based on the following commits from file-roller,
https://git.gnome.org/browse/file-roller/commit/?id=2575177ac037d2a8d8f3056b10685928d80d6275
https://git.gnome.org/browse/file-roller/commit/?id=f26caa6d5b76d406976ea78630fbaae4c8126a2e
Merge pull request #21 from infirit/unarchiver

Add unarchiver support