Improve JSON endpoint error pages

[fluffy-critter]

Whenever working on an Angular component, trying to debug failures with JSON blob retrieval becomes quite the nightmare due to the way that error pages are handled in Catalyst. It would be very helpful if JSON endpoints were to somehow override the error handler to only return a smaller JSON blob that contains the actual error message and maybe the top N entries of the stack trace.

[fluffy-critter]

One possibility: if there’s a way to override the error handler and have it do a new behavior based on the request’s Accept: header