Per-request view paths and layouts

The attached patch addresses some issues with layouts when they are being used with per-request view paths. The current implementation always refers to the class level view paths rather than the instance level view paths resulting in missing template errors when using template names that don't match between different view paths

The only issue that isn't address is the auto-detection of layouts which would require scanning of template directories on every request which isn't desirable. Since the main use case for per-request view paths is for some kind of theming of content then having consistent names for auto detection between different themes is probably what would be preferred anyway.