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