Display Custom Error Messages On "model.save" Failure

[mattoberle]

clay/amphora implements error handlers that return the following JSON when an exception is encountered (eg. during model.save):

{ "message": "The Error's Message Here", "code": 500 }

When Kiln encounters these errors it displays a generic Error publishing article in the "snack bar".

This happens here while saving a component:
https://github.com/clay/clay-kiln/blob/master/lib/component-data/actions.js#L52-L71

And happens here on page publish:
https://github.com/clay/clay-kiln/blob/master/lib/drawers/publish-page.vue#L305-L314

Kiln has the context to display a more detailed message via e.response:

clay-kiln/lib/core-data/api.js

Lines 114 to 116 in 8718789

	let error = new Error(res.statusText);
	error.response = res;

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Rather than teaching editors to open their browser's developer tools to retrieve a console log, we should include additional information in the message itself.

This could be accomplished in two ways:

1. Grab the response JSON and include the message attribute (low-effort, kiln-only change).
2. Assign a uuid in clay/amphora's error handler, log it in Amphora, display it in Kiln.