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
Use yelp-tools instead of mate-doc-utils
Merge pull request #23 from infirit/yelptools

Use yelp-tools instead of mate-doc-utils
Merge pull request #21 from infirit/unarchiver

Add unarchiver support
Add transifex configuration file
Sync translations with transifex
fr-window: Assertion check to prevent ptr dereference

* clang static analysis shows that if this function
  is called with file_list set to NULL, it would be
  dereferenced.
Merge pull request #25 from kallisti5/master

fr-window: Assertion check to prevent ptr dereference
update remaining file-roller->engrampa name change