Enhances API urls:
  - Moves backend urls to localstorage backend module
  - Start at root uri / not under not wanted /files/ uri namespace
Updates _get_parent method:
  - if not path > no parent it s the root dir
  - but parent path can be ''
Sets unused columns to null for non approximative filtering.
Moves download/<path> urls in first place otherwise it would be considered as file item url.
Updates parent path filtering.
Updates fixtures and tests.
Merge pull request #18 from open-nuage/better_smaller_urls

Better smaller nicer urls.