WinRT: Improve key handling

Change mapping strategy to use operating system's key translation.
Do not map character keys, but do map meta keys.
This replaces the existing key mapper, so squash with daa3d5.

Change-Id: I414027b9a58f702701faf2b7f7d7a9488e8e51a2
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>