Misc. improvements for ordering batches, purchases

also we now show handler's description when executing batch

tailbone/templates/batch/view.mako

@@ -211,6 +211,12 @@
                       </header>
 
                       <section class="modal-card-body">
+                        <p class="block has-text-weight-bold">
+                          What will actually happen when this batch is executed?
+                        </p>
+                        <p class="block">
+                          ${handler.describe_execution(batch) or "TODO: handler does not provide a description for this batch"}
+                        </p>
                         <${execute_form.component} ref="executeBatchForm"></${execute_form.component}>
                       </section>