Do not save an xblock after rendering the Studio view.

TNL-399

After extended conversations with @explorerleslie , @cpennington , and @dmitchell , Leslie decided that we should remove the save call after rendering the Studio view. This fixes TNL-399 (which, interestingly, was not an issue for split modulestore).

Note that there is still a chance that the "Published" vs "Unpublished Changes" status will get out of date, if an xblock is doing AJAX callbacks. The xblock ajax handler in component.py also does a call to update_item. As far as I know, this only impacts the acid xblock, which is not used by any courses. We have no mechanism at this point to know that the client side needs to re-fetch data in this case.

Note also that clicking "Save" on the Studio view editor will always create a draft version in the old draft modulestore, even if there are no actual changes (this is not true for split modulestore). I have created a story to make the behavior consistent, https://openedx.atlassian.net/browse/TNL-632.

@andy-armstrong and @zubair-arbi Please review.
I have run the test manually with draft mongo to ensure it passes (bok choy tests run with split in Jenkins).

I put in a JIRA ticket to have the Lettuce and Bok Choy tests run with all supported modulestores. I think that would be a better way to get this coverage, and it would be most helpful to prevent regressions.

https://openedx.atlassian.net/browse/TE-546