Milton.io ContentGenerator that renders a themed HTML error page instead of Milton's plain default response body. Registered as the server's content generator in ApplicationStarter, it is invoked by the Milton HTTP handling pipeline whenever a response needs a body written for a given status. For GET requests to paths that are not obviously static assets (js, css, png, json, ico), it looks up the current tenant's root folder and renders the "error/{status code}" theme template through an ErrorResource wrapping the failing resource and status. All other requests, and any failure while rendering the themed page, fall back to Milton's default SimpleContentGenerator.

Implements: ContentGenerator