Capturing task errors

[RealOrangeOne]

Because the result of a task must be JSON serializable, it's not possible to pass the exception back to the TaskResult to expose to the user. For failed tasks, .result will always be None.

How important is it that the exception be retrievable? Is there an alternative way to serialize the exception (even just its name) to pass back instead?

The exception is handled using logger.exception, allowing it to be obtained by monitoring addons (eg Sentry).

[RealOrangeOne]

Moving discussion to #63