Revert "Don't require applications to declare metatypes."

This reverts commit 5679a86968a6a26f8427b9c979f89f6ea5198d2f

Change was source incompatible.

Change-Id: Ied25ca3503a41e498a5c9b710e7a0dd3787bbe89
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>