Configuration utilisateur K-Fêt

Old configuration(/settings), based on Settings model, system is deleted: SettingsForm, Settings.
New system use django-djconfig module.

K-Fêt configuration

• kfet.config module provides kfet_config to access configuration concerning kfet app.
• Views, forms, models, etc now use this object to retrieve conf values.
• Views no longer add config values to context, instead templates use kfet_config provided by a new context_processor.
• Enhance list and update views of settings.
• Fix: settings can directly be used without having to visit a specific page...

Misc

• Delete some py2/3 imports
• Delete unused imports in kfet.models and kfet.views
• Some PEP8 compliance