New version of django fix the RuntimeError while saving wepb file.

The patch will not be applied to Django 1.8

Ref: https://www.djangoproject.com/download/#supported-versions

Ref: https://github.com/django/django/pull/10331

\d allows numbers from other digit systems, so urls like: http://demo.getpinry.com/१७/ are possible. This could lead to some nasty security issues in the future (ie. if you try to use pin number without using `int(...)`).

Removed pins django app, and moved code to the core. Moved user related
code out of core to the users app.

Rewritten register view using CBV approach, and added a authenticate/login
call after form has been validated and user created. Fixes #65