Refactor ExceptionRenderer.

The ablility to have methods per exception has been removed. That feature
wasn't DRY.
Consolidate Error\BaseException and Error\Exception into a single class.
Use short param type.
Remove Exception coercion.

Just change error message and template instead.
Tweak template name generation.
Move reponse header setting.
Add back feature to have exception renderer methods for matching exceptions.
Merge pull request #3344 from ADmad/3.0-exception

3.0 exception