v0.4.0 : Add user account

This PR release adds some new features :

• Users need to be authentified to access the app
  • Introduce login page and logout feature
• Only admin users can access those pages
  • Users page
  • Categories page
• Database has been refactored :
  • User can have their own collections
    • User collections are embedded into users and synced thanks to cloud function
  • Users can now only access their data thanks to the database rules
• Add new make docker-deploy-functions target to easily deploy firebase functions