Added UI elements to add/remove Scenarios to various objects (#51)

Fixes #23

Co-authored-by: Tim Lorsbach <tim@lorsba.ch>
Reviewed-on: enviPath/enviPy#51

templates/actions/objects/compound.html

@@ -7,6 +7,10 @@
         <a role="button" data-toggle="modal" data-target="#add_structure_modal">
             <i class="glyphicon glyphicon-plus"></i> Add Structure</a>
     </li>
+    <li>
+        <a role="button" data-toggle="modal" data-target="#set_scenario_modal">
+            <i class="glyphicon glyphicon-plus"></i> Set Scenarios</a>
+    </li>
     <li>
         <a class="button" data-toggle="modal" data-target="#delete_compound_modal">
             <i class="glyphicon glyphicon-trash"></i> Delete Compound</a>