WIP: Simplify error handling

[mabar]

• Dropped IErrorDecorator - response decorators should now implement only IResponseDecorator to e.g. add CORS headers, as would user expect
• Single class is responsible for decorating error into response and is always required
• Transformers from apitte/negotiation will receive only ApiException
• Exception from SnapshotException is unwrapped for logging
• Message from previous exception of ApiException is logged instead of ApiException message, if previous exception is available
• Generic error message (Application encountered an internal blah blah...) moved into ServerErrorException and could be modified via static $defaultMessage

[mabar]

Most of the issues resolver by separate PRs, unification of error transforming classes will need some architectural changes