chore(exception)!: Enhance exception handling

- Replace http://localhost/ with http://example.com[/]

 because localhost ist a possible valid host and therefore confusing for users. Considered info-removed-for-privacy-reasons.com (or something similar), but there is no guarantee that this domain is not registered. example.com can by definition not be registered.
- Unify way to create a response on an exception by passing the whole exception object into the helper method
- Use HTTP 900 for unknown exceptions to distinguish other proprietary status codes: HTTP 520 is for example used by Cloudflare. Note that HTTP 900 is also not standardized.

Signed-off-by: Stefan Niedermann <info@niedermann.it>