1.1 Content Update!

This update adds the content used in the 1.1 Update, featuring Mystery Box and Powerups. By updating content to this version, you will be able to use the 1.1 development version from Github.

- Added Mystery Box & Teddy Bear models
- Added Powerup models
- Added Death Machine and Revive Syringe models (from nZ)
- Added HUD Icons for all base powerups
- Added Announcer sound files for all base Powerups and Mystery Box

- Added missing Discord Promo banner image
- Added various (currently unused) logo images: nZU_Icon_box.png, nZU_Logo.png, nZU_Logo_Text.png
- Update "Spawns" Zombie Rig to have all animations use 'snap' (meaning they don't blend together)

- Added missing low health overlay
- Updated VGUI skin to allow panels to have background colors
- Updated Zombie Models to have hitboxes to allow headshot points
- Update Zombie Models to have footstep events
- Updated Zombie Models to make elemental and special movement animations loop

Added new model for Barricades.

Added missing Electricity Switch model and materials.