feat: restore css and js blocks

[wesleyboar]

Overview

Restore {% block css %}{% endblock %} and {% block js %}{% endblock %}.

These are simple and immediately understood. There were in the original code. I removed them after my over-engineering took over. I intend to migrate to using them more often, and perhaps to only using them. The Core-CMS is too complicated. It is time to simplify it.

Related

• required by https://github.com/TACC/Core-CMS-Resources/pull/193

Changes

• added {% block css %}{% endblock %}
• added {% block js %}{% endblock %}

Testing & UI

N/A

This adds a backwards-compatible invisible feature that is already well-tested with other `{% block … %}`'s.