Destroy Annotator app before storing page into brwoser cache

If we do not destroy annotator app before storing the page at
browser cache we will unnecesarily initialize annotations twice (or
more) duplicating Annotator HTML markup and causing
unexpected  errors.

Without this commit you will find an error when restoring a page with
annotator, you can click on any annotation and you will see the annotation
comments are being loaded twice.

IMO this is an idempotency issue within Annotator JS library.

app/assets/javascripts/application.js

@@ -172,6 +172,7 @@ var destroy_non_idempotent_modules = function() {
 
   App.Datepicker.destroy();
   App.HTMLEditor.destroy();
+  App.LegislationAnnotatable.destroy();
 };
 
 $(document).on("turbolinks:load", initialize_modules);

app/assets/javascripts/legislation_annotatable.js

@@ -226,6 +226,11 @@
           });
         });
       });
+    },
+    destroy: function() {
+      if ($(".legislation-annotatable").length > 0) {
+        App.LegislationAnnotatable.app.destroy();
+      }
     }
   };
 }).call(this);

spec/system/legislation/draft_versions_spec.rb

@@ -237,6 +237,23 @@ describe "Legislation Draft Versions" do
 
       expect(page).to have_content "Comment can't be blank"
     end
+
+    scenario "When page is restored from browser cache do not duplicate annotation handlers" do
+      create(:legislation_annotation, draft_version: draft_version, text: "my annotation")
+
+      visit legislation_process_draft_version_path(draft_version.process, draft_version)
+
+      expect(page).to have_css(".annotator-hl", count: 1)
+
+      click_link "Help"
+
+      expect(page).to have_content "CONSUL is a platform for citizen participation"
+
+      go_back
+
+      expect(page).to have_content "A collaborative legislation process"
+      expect(page).to have_css(".annotator-hl", count: 1)
+    end
   end
 
   context "Merged annotations", :js do