Added tox

https://testrun.org/tox/latest/
Fixed failing migrations

Migrations where fixed so they use the correct user model depending on
the running environment
Merge branch 'south-1' into softdelete

Conflicts:
	requirements.txt
	setup.py
Updated django-safedelete requirement
Maked softdelete optional

Using `NOPASSWORD_SOFTDELETE` settings is posible to choose from
`django.db.models.Model` or `SoftDeleteMixin` as `LoginCode` base class
Added Django 1.6 support

Nothin in the code changed. Travis ant tox config files where updated
to run tests for Django 1.6.2