Consolidate base templates

[AdrianDAlessandro]

I'm struggling to see the point of this additional main/base.page.html template. It's used in most, but not all, of the templates under main/pages, the only difference between this and main/base.html is this container div, which feels like a lot of repeated code for one container.

Maybe it makes more sense to make this extend main/base.html and then have something like:

{% block content %}
    <div class="container my-5 pt-5">
        {% block page_content %}
        {% endblock page_content %}
    </div>
{% endblock content %}

Also, the fact it's used inconsistently also might be why I'm seeing the breadcrumbs not line-up from page to page? If the definition of a page is that we have the breadcrumbs at the top, maybe we should include that in this base.page template?

Originally posted by @AdrianDAlessandro in #480 (comment)