Add log to Azure table when JS fails

[bradunov]

We currently have an exception handler for uncaught errors but it only displays an error message in dev mode. We need to log it in a table for wider deployments.

[bradunov]

Currently there is an implementation of window.onerror in question.py that prints JS error on screen if it happens. We should implement one that logs it onto Azure. It should capture question state, if exists.