Failure to login to XMPP should be shown in the UI for the login screen, or handled by the UI

[willscott]

Issue by infmally from Wed Oct 30 19:06:20 2013
Originally opened as https://github.com/UWNetworksLab/UProxy/issues/114

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To reproduce the issue:

• Login to XMPP, but put the wrong password in.

Observe:

• Looks like it works ok, you get a loading screen in the roster view.
• But go to the settings and see you are not logged in.

Suggested behaviour:

• Show an error in the login view.

[willscott]

Comment by ryscheng from Wed Oct 30 19:07:54 2013

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uzimizu and I were planning on coordinating on error codes for identity. Got tabled during summit.

[scouttle]

Need a design for reporting the error; should be addressed as part of #83.

[dborkan]

Done