Rename API modules
Add a fipes_file module
Add a fipes_user module
Replace code related to files and users by the new modules functions
Implement the fipes_file:find_by_fipe function
Implement the fipes_owners:notify function
Fix a minor bug when unregistering a user
Import all the fipes_user functions into fipes_owners
fipes_owners becomes fipes_owner
Remove the fipes_user module
Minor refactoring for fipes_owner
Implement the fipes_downloader module

fipes_downloader has the same purpose as fipes_owner but is dedicated for
downloaders only
Merge branch 'refacto/modules' into develop