Add sidebar links with external icons

Undergraduate sidebar:
- Added Math Collaborative Learning Center (above DRP)
- Added Geometry Lab (below AWM@UVa)

Graduate sidebar:
- Added AMS Grad Student Chapter (above Graduate Students Seminar)

All with external link icons to indicate cross-section navigation

Author: lenis2000

_includes/g_sidebar.html

@@ -13,6 +13,7 @@
         <a class="list-group-item list-group-item-action {% if page.permalink ==  pg.permalink %}active{% endif %}" href="{{pg.url}}">{{pg.title}}</a>
     {% endif %}
     {% endfor %}
+  <a class="list-group-item list-group-item-action" href="{{site.url}}/ams_chapter/">AMS Grad Student Chapter&nbsp;<span class="fa-solid fa-up-right-from-square" aria-hidden="true"></span></a>
   <a class="list-group-item list-group-item-action" href="{{site.url}}/seminars/gradsem/">Graduate Students Seminar&nbsp;<span class="fa-solid fa-up-right-from-square" aria-hidden="true"></span></a>
 </div>
 

_includes/ug_sidebar.html

@@ -7,8 +7,10 @@
         <a class="list-group-item list-group-item-action {% if page.permalink ==  pg.permalink %}active{% endif %}" href="{{pg.url}}">{{pg.title}}</a>
     {% endif %}
     {% endfor %}
+  <a class="list-group-item list-group-item-action" href="{{site.url}}/undergraduate/MCLC/">Math Collaborative Learning Center&nbsp;<span class="fa-solid fa-up-right-from-square" aria-hidden="true"></span></a>
   <a class="list-group-item list-group-item-action" href="{{site.url}}/drp/">Directed reading program&nbsp;<span class="fa-solid fa-up-right-from-square" aria-hidden="true"></span></a>
   <a class="list-group-item list-group-item-action" href="{{site.url}}/awm/">AWM&commat;UVa&nbsp;<span class="fa-solid fa-up-right-from-square" aria-hidden="true"></span></a>
+  <a class="list-group-item list-group-item-action" href="{{site.url}}/geolab/">Geometry Lab&nbsp;<span class="fa-solid fa-up-right-from-square" aria-hidden="true"></span></a>
   <a class="list-group-item list-group-item-action" href="https://sites.google.com/view/maps-at-uva">Math Peer Support&nbsp;<span class="fa-solid fa-up-right-from-square" aria-hidden="true"></span></a>
   <a class="list-group-item list-group-item-action" href="{{site.url}}/seminars/mathclub/">Undergraduate Math Club&nbsp;<span class="fa-solid fa-up-right-from-square" aria-hidden="true"></span></a>
 </div>