Layer Categories: UI updates based on new mocks

1. Add a default layer category icon (same icon as the layers button on the sidebar)
2. Update expand/collapse toggle to use caret instead of chevron

src/js/templates/maps/layer-category-item.html

@@ -1,13 +1,15 @@
 <div class="<%= classNames.metadata %>">
   <span class="layer-category-item__icon-and-label">
-    <span class="<%= classNames.icon %>" />
+    <span class="<%= classNames.icon %>">
+      <svg xmlns="http://www.w3.org/2000/svg" fill="currentColor" viewBox="0 0 24 24"><path d="m3.2 7.3 8.6 4.6a.5.5 0 0 0 .4 0l8.6-4.6a.4.4 0 0 0 0-.8L12.1 3a.5.5 0 0 0-.4 0L3.3 6.5a.4.4 0 0 0 0 .8Z"/><path d="M20.7 10.7 19 9.9l-6.7 3.6a.5.5 0 0 1-.4 0L5 9.9l-1.8.8a.5.5 0 0 0 0 .8l8.5 5a.5.5 0 0 0 .5 0l8.5-5a.5.5 0 0 0 0-.8Z"/><path d="m20.7 15.1-1.5-.7-7 3.8a.5.5 0 0 1-.4 0l-7-3.8-1.5.7a.5.5 0 0 0 0 .9l8.5 5a.5.5 0 0 0 .5 0l8.5-5a.5.5 0 0 0 0-.9Z"/></svg>
+    </span>
     <span class="layer-category-item__label">
       <%= label %>
     </span>
   </span>
   <span class="layer-category-item__expand-toggle">
-    <i class="icon-chevron-up <%= classNames.collapsed %>"></i>
-    <i class="icon-chevron-down <%= classNames.expanded %>"></i>
+    <i class="icon-caret-up <%= classNames.collapsed %>"></i>
+    <i class="icon-caret-down <%= classNames.expanded %>"></i>
   </span>
 </div>
 <div class="<%= classNames.layers %>" />