serve: Rewrite of the Server-Sent Event code for build notifications. At the moment the server monitors the asset directories, and notifies the browser when an asset has changed and has been re-processed. * Fix issues around long-running requests/threads which mess up the ability to shutdown the server correctly with `CTRL-C` (see comments in code). * Move the notification queue to each SSE producer, to support having multiple pages open in a browser. * Add JS/CSS for showing quick notifications about re-processed assets. * Add support for hot-reloading CSS and pictures that have been re-processed.

{% extends "default.html" %}

{% block content %}
<div class="container">
    <section class="col-md-8">
    {{ content|safe }}
    </section>
    <aside class="col-md-4">
        {% include 'inc/family-sidebar.html' %}
    </aside>
</div>
{% endblock %}