Updated to Python3.  Use extra stuff from github.com/radiantflow

Signed-off-by: JP-Ellis <coujellis@gmail.com>
Use CDN instead of packing Select2.

Instead of packaging Select2 along with this, use a CDN to get the
Select2 JS and CSS files.

Added templatetags in order to easily add the required dependencies
(implementation taken from the django-bootstrap3 plugin).

Also fixed an issue with the Select box having an invalid `input_type`.

Lastly, a litte JS cleanup.

Signed-off-by: JP-Ellis <coujellis@gmail.com>