Performance Update and WMR support

Hey everyone,

This update adds Windows Mixed Reality support and addresses issues
that some users experienced. In particular:

• Hand movement has now been improved.
• Overall performance has been improved.
• The grip button on Valve Knuckles controllers can now be used to grab objects.
• The visual quality of the "normal graphics" setting for Rift S has been improved.

Thanks for playing, stay tuned for more updates and watch out for the
Krampus Killer!