fix(shared): button block not respecting icon

shared/templates/styleguide/2.3.x/blocks/button_block.html

 {% load wagtailcore_tags wagtailimages_tags %}
 {% firstof self.page.url self.link as target %}
-
-<a href="{{ target }}" class="btn btn--{{ self.color }} {% if self.hoveractive %}btn--hoveractive{% endif %} btn--autowidth text-{{ self.size }}"
+<a href="{{ target }}" class="btn btn--{{ self.color }} {% if self.hoveractive %}btn--hoveractive{% endif %} {% if self.icon %}btn--icon{% endif %} btn--autowidth text-{{ self.size }}"
 >
+    {% if self.icon %}
+        <div class="btn__body-wrap">
             <div class="btn__body ">{{ self.title }}</div>
+            <div class="btn__icon "><i class="ico--{{ self.icon }}"></i></div>
+        </div>
+    {% else %}
+        <div class="btn__body ">{{ self.title }}</div>
+    {% endif %}
 </a>