Port base template to jinja2

[gregplaysguitar]

Django looks in the jinja2 subdirectory, so this should work out of the box with the jinja2 template engine, if APP_DIRS is set to true in the template settings, i.e.

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.jinja2.Jinja2',
        'DIRS': ['[site template dir]'],
        'APP_DIRS': True,
    },
]