UI + Model Loading

[Tyler-Lentz]

Closes #44

This PR implements both the initial UI implementaiton, and it also includes in Anthony's initial model loading logic.

Setup

1. You need to manually copy in the models into your assets folder. Check the google drive and just copy all of the models from there into assets/graphics
2. If you have gdown installed (should be easy on linux / max, idk about windows) then make pull_models should download them to the right location

Features

1. Title screen, lobby browser, lobby menu, pause menu in game
2. render player model with coco's model!

Notes / Todos

1. You can technically load in sprites/images, but not position them yet. That will be in another PR
2. Lighting for models
3. better / more systematically align player model with floor
4. Allow you to specify an IP in the lobby browser, because right now you can only connect if you can receive the broadcast packets