WIP: Improve demo

[BastiaanOlij]

Working on some new enhancements found a few bugs in the demo code.

Updated upstream OpenVR and vr-common libraries and now working on tweaking the demo a bit.

[BastiaanOlij]

Added a bunch of assets from Kenney to create a better environment and a nice HDRI for the sky. I may swap out the HDRI for something a little more daytime.

Working on getting a weapon to work and providing something to shoot at.

[BastiaanOlij]

Made a bunch of improvements, you can now reload the gun, the bullet show a trail to see what you're shooting at, I added a muzzle flash and added some crappy sounds :)

[BastiaanOlij]

I've already applied updating the OpenVR and vr-common to the master branch and made a few tweaks to the demo just to fix it up.

I'm thinking of moving the demo I was working on here into its own repository, it's become way to big as a sample project.
I might just add some simple things to the existing demo so you can pick something up and that sort of thing.