Deprecate bulma in favor of normalize and milligram

Deprecate the bulma css framework in favor of normalize and
milligram. Adapt the templates to work with the new css libraries.

templates/shortcodes/modal.html

@@ -6,11 +6,11 @@
 {% endif %}
 {% set thumb = resize_image(path=full_path, width=400, height=400, op="fit") %}
 
-<div class="item">
+<div>
   <a href="#{{ path }}">
-    <img src="{{ thumb.url }}"/>
+    <img class="modal-thumbnail" src="{{ thumb.url }}"/>
   </a>
-  <div class="lightbox image has-text-centered" id="{{ path }}">
+  <div class="modal" id="{{ path }}">
     <a href="#" class="close">
       <span class="spacer"></span>
       <img src="{{ path }}" />