[iso-core] always default to showing an error message
[iso-core] always default to showing an error message

Summary:
Don't show the "Unknown error contact support" thing anymore. Show the raw
error. Also add the message we show the user and the code we think the
error is to the status page

Test Plan: manual

Reviewers: halla, spang, juan

Reviewed By: juan

Differential Revision: https://phab.nylas.com/D4458

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