Bug/654 redirect to stats.php on disconnect

[JahleelAbraham]

The issue outlined by #654 is caused when the client disconnects from the internet and can no longer send a request to /ajax/stats.php. The code that causes this is a commit made to solve issue #474 which sends the entire browser to the URL /ajax/stats.php/ because the background request failed.

The solution proposed by this PR works around both of these issues by create a way to create exception to the redirection when the request fails by simply passing false to the optional parameter redirectOnFail.

This is by no means a proper solutions and a better solution for both issue #654 and #474 might be needed to be discussed.

[andrey-utkin]

Please add true/false for the new argument in all other call sites. Or is there only one?

[andrey-utkin]

Thanks. Looks good to me.
I am going to run a test with these changes and merge if it's all good (which it should be, given the clarity of changes).
(With regard to git history, I am going to squash the second and third commits into the first.)

[andrey-utkin]

Tested this manually, the fix holds up - leaving the web page to idle for a long time, and deliberately disconnecting machine (shortly, or until requests time out) doesn't cause any redirect. Merging.