Support editing obf / opf and opff taxonomies

[alexgarel]

What

• This year we gonna work on Open (Product|Beauty|Pet Food) Facts and taxonomy editor will be useful to that purpose.
• Taxonomies for those projects are stored in specific sub-folders: taxonomies.obf for example.
• We must insure we are able to edit those taxonomies.
• This only have to do with the import / export phase where we must be able to handle the directory.

Part of

• 🎯 What can i work on ? (Tracker) #30