feat: add slug to AEP page

Since we're moving toward slugs as the canonical identifier
rather than aep numbers, making the more prominent on the
AEP page.

Also adding bold to the categories in the navigation to
help better distinguish category vs AEP.

aep_site/support/templates/aep.html.j2

@@ -22,6 +22,7 @@ AEP-{{ aep.id }}: {{ aep.title }}
   {# Wikipedia-style info table. -#}
   <table id="aep-summary">
     <tr><th colspan="2">{{ aep.title }}</th></tr>
+    <tr><td>Slug</td><td>{{ aep.slug }}</td></tr>
     <tr><td>Number</td><td>{{ aep.id }}</td></tr>
     {% with permalink = site.base_url + aep.relative_uri -%}
     <tr><td>Permalink</td><td><a href="{{ permalink }}">{{ permalink.lstrip('htps')[3:] }}</a></td></tr>
@@ -55,7 +56,7 @@ AEP-{{ aep.id }}: {{ aep.title }}
     {% include 'includes/breadcrumb.html.j2' %}
   {% endwith -%}
   {% include 'includes/state_banners/' + aep.state + '.html.j2' ignore missing %}
-  <h4 class="aep-number">AEP-{{ aep.id }}</h4>
+  <h4 class="aep-number">{{ aep.slug }} (AEP-{{ aep.id }})</h4>
   {{ aep.content.html }}
   {% include 'includes/footer.html.j2' %}
 </section>

aep_site/support/templates/includes/nav.html.j2

@@ -14,7 +14,7 @@
     {# Individual AEPs in this scope. -#}
     <li class="nav-item nav-item-header">AEPs</li>
     {% for cat in site.scopes[scope_code].categories.values() -%}
-      <li class="nav-item">{{ cat.title }}</li>
+      <li class="nav-item"><b>{{ cat.title }}</b></li>
       {% for aep in cat.aeps.values() -%}
         <li class="nav-item{% if path.split('/')[-1] == '{:d}'.format(aep.id) %} nav-item-active{% endif %}">
           <a href="{{ site.relative_uri }}/{{ aep.id }}">