Add film noir elements

[PavlosMak]

This branch resolves 2 issues related to giving the game an even more noir aesthetic. Namely, this PR introduces:

• Film grain post-processing. This was implemented by adding a post-processing override to a volume attached in the main camera prefab. From there the parameters can be fine-tuned.
• Made the aspect ratio be 4:3 to match the original noir films. This was implemented by using the LetterBoxer package and adding the LetterBoxer script in the main camera prefab again. From there the parameters can be changed and tuned but for now, as mentioned above, I have set it to 4 over 3.

Closes #44 and #46.

[howchen217]

Everything works as intended, and I added vignette and a bit of lens distortion, which i think is a nice touch, need you guys to have a look though