Setup basic Revision History page

Sets up paper_trail tracking in important models

and add conference_id to versions for storing conference_id
of conference related objects  as metadata.This will help in querying
for versions related to conferences.

Fix issues with factories & event types initialization.Import paper_trail testing helpers
Fix bug: Creating an event creates a useless version with event update

Add revert and view changes features to revision history

app/assets/javascripts/osem-datatables.js

@@ -7,6 +7,11 @@ $(function () {
       pagingType: 'full_numbers',
       "lengthMenu": [[25, 50, 100, -1], [25, 50, 100, "All"]]
     });
+
+    $('#versionstable').DataTable({
+      pagingType: 'full_numbers',
+      order: [[ 0, 'desc' ]]
+    });
   });
 });