ArcGIS Server token request error handling with retry

[gassc]

Currently, if the application can't get a token from the ArcGIS Server endpoint (on ROK Tech), we only show a message to the effect of "couldn't get the token, sorry". It doesn't attempt to retry the request.

Since the problem is fairly rare, a short term solution is in cfe8ef7, which advises the end-user to refresh the browser window. This almost always works.

The real solution of course is to attempt to retry acquiring that token using a randomized and exponential back-off and retry approach.