[Feature] Engineer Pathway (#256)

Co-authored-by: Tim Lorsbach <tim@lorsba.ch>
Reviewed-on: enviPath/enviPy#256

templates/actions/objects/pathway.html

@@ -41,6 +41,14 @@
     <i class="glyphicon glyphicon-floppy-save"></i> Download Pathway as Image</a
   >
 </li>
+<li>
+  <a
+    role="button"
+    onclick="document.getElementById('engineer_pathway_modal').showModal(); return false;"
+  >
+    <i class="glyphicon glyphicon-cog"></i> Engineer Pathway</a
+  >
+</li>
 {% if meta.can_edit %}
   <li>
     <a