show "Reload required" error if app JS is redeployed after user's initial page load

Created by: sqs

• fix #1760 (closed)
• also other commits to fix other related issues

In https://github.com/sourcegraph/sourcegraph/issues/1760#issuecomment-453235933 @nicksnyder recommended just removing chunking altogether. I found an easy way to retain chunking (which improves page load times significantly) without the problems I worried about at https://github.com/sourcegraph/sourcegraph/issues/1760#issuecomment-453224286. Plus, this is a more comprehensive solution. Reverting to our previous situation (with 1 main chunk and then chunks for GraphiQL (API console) and Monaco) would still cause this problem to exhibit itself after a redeploy if the user tried to navigate to the API console or the Monaco editor. Now they will be prompted to reload in all cases when it is necessary.