Milestone M30 updates

Let's go through what we got done in Milestone M30 (Feb 10 - Feb 23).

• We fixed final set of issues with 404 URLs from academy.bigbinary.com, by setting up the right redirection logic trickling down to chapters and pages, for the courses that don't exist anymore.

• We fixed an issue with evaluation of Promises in JavaScript where despite the user getting the right output, the code was judged not passed. We fixed some edge cases in our evaluation logic to fix this.

• Multiple issues over the last few weeks, related to students not seeing their progress correctly tracked in courses were resolved this week after a little observation. We fixed it by adding an index to avoid possible duplicates, and also by considering the logic that some progress records may be outdated because of the pages/chapters themselves having been unpublished/removed from the content.

• We made the code diffs that get displayed when a student's code doesn't pass the evaluation, a little more informative and highlighting what needs to be fixed.

• We had been observing the /services_health_check endpoint itself timing out and causing honeybadger issues over the last few weeks. On observation, we found that if Elasticsearch is unresponsive, the underlying health check command waits for a long time and causes the entire health check itself to throw a timeout error. We fixed it by adding a timeout to Elasticsearch check at neeto-commons-backend level, so it fails fast if its not responding. This would also work for all other apps that have Elasticsearch in their stack.