add base template

Add base template (with all imports) for extends.

Sample:

    # my template

    extends "foundation/base.html"

    {% block title %}My page{% endblock %}

    {% block css %}
        {{ block.super }}
        <link rel="stylesheet" href="{{ STATIC_URL }}path/to/my.css"></script>
    {% endblock %}

    {% block site %}
        All body content here!
    {% endblock %}

    {% block js %}
        {{ block.super }}
        <script src="{{ STATIC_URL }}path/to/my.js"></script>
    {% endblock %}