Move KFetConfigForm to kfet.config

Import in `ready` method of kfet app config of `kfet.forms` may be
annoying because it starts executing `__init__` methods of fields.
Causing failures if these methods does DB calls, as `ready` may be
called before applying migrations.

kfet/migrations/0054_delete_settings.py

@@ -4,7 +4,7 @@ from __future__ import unicode_literals
 from django.db import migrations, models
 import django.db.models.deletion
 
-from kfet.forms import KFetConfigForm
+from kfet.config import KFetConfigForm
 
 
 def adapt_settings(apps, schema_editor):