Adding occlusion and physics

[Abb4]

• adjusted sandbox level, which uses kenney tilemap. Note: I did not adjust all tiles, just the ones we need for prototyping
  • added occlusion layer (fixes #9)
  • added physics layer (fixes #8)
  • adjusted navigation layer to avoid the ai getting stuck (fixes #29 for now, need better solution for the future, see comment below or specifically https://github.com/Abb4/earie-treasures/issues/31)

[Abb4]

I noticed that the AI character was getting stuck on player and walls, especially wall corners.

Apparently godot does not support static obstacle avoidance in 2d even though it does do that in 3d.

Another problem is that I want to define collision inside of the tilemaps because it is nicer. But assembling the navigation polygon from tilemaps could prove difficult. We need to sync with navigation server, extract the nav polygons from the individual tiles inside of the tile map, collect them into a single polygon and finally shrink the polygon and send it to the server as a new map. Then we may also need to assign the map to all the actors that are using it for pathing requests.

All in all I created a new issue to collect info: #31