PixiJS Implementation

[rebeccasjoen]

[x] Communication between frontend Pixi og server
[x] New character added when new client joins
[x] Move character with keyboard
[ ] Fix movement: up is up and down is down
[ ] Fix slow movement speed
[x] Update with new changes to contract (communication object on frontend)
[ ] Add linear algebra library (to get angle between vectors)
[ ] Coordinate system with origo in the middle of the game world
[ ] Rotate character following mouse cursor
[ ] Rotate using rotation vector from server (rotation vector must be updated correctly on server)