Fixes based on peer feedback

• Added doppler effect to Zombie sounds
• Increase UI scale on the main menu
• Player walk speed increased from 3 > 4
• Player sprint speed increased from 5 > 6
• Player jump force increased form 125 > 135
• Sound added for when buying perks
• Sound added when interacting with Ammo box
• Selected weapon UI scaled down
• Front door added to the environment