Bug: Autodiscover GetUserSettings does not return descriptive errors

[gautamsi]

based on @jackiehluo's comment on #23, need to add descriptive errors when there is issue in completing the request.

[jackiehluo]

@gautamsi Yes, that would be super helpful overall! In general, I've found that a lot of my failed requests just fail silently or return undefined, which makes it hard to debug.

[gautamsi]

I have checked my code, Autodiscover errors are not correctly thrown. I have already fixed ExchangeService code to properly return error in case of failures.

[gautamsi]

autodiscover is re-written, this should be non-issue now. reopen if needed