Present errors gracefully, with actionable info

Related to https://github.com/Duke-GCB/D4S2/issues/206, but I find that most API error codes are not handled gracefully by datadelivery-ui

- Visiting a delivery that is not found (e.g. https://datadelivery.genome.duke.edu/deliveries/phony-id) results in an empty page, and some JS errors in the console. This should be a helpful 404-style page
- detail message strings provided by the API are represented as `[Object object]` in the Ember Data error response, suggesting they're not being deserialized correctly. This is difficult to see in the current state, since the errors aren't really being displayed