Resolve "Use icons instead of plain text"

Closes #80 (closed)

biscuit/core/templates/core/edit_group.html

@@ -23,7 +23,7 @@
     {% csrf_token %}
     {% bootstrap_form edit_group_form %}
     <button type="submit" class="btn btn-dark">
-      {% blocktrans %}Edit{% endblocktrans %}
+      <span class="mdi mdi-pencil"></span>
     </button>
   </form>