Tweaks to address some issues found during testing

Addresses these issues found during testing for #908:

- Remove trans tag from JS file string.
- Give "cancel" button some breathing room above it on update page.
- Show "Loading" rather than "null" when update process is starting up.
- Show UpdateProgressLog in Django admin interface.
- More meaningful messages when there's an error checking update status.

Also some auto-whitespace trimming, it seems; sorry.