Shadows + Jolt Physics for browser version

New:
- Enabled godot 4 shadows for html exports (they kinda ruin the games aesthetic though, so I'll likely might revert or at least tweak this   change).
- Switched physics engine to Jolt Physics (which very recently started offering html web browser support).
 
Pending:
- Browser lag spike when hitting buildings.
- Remove shadows.
- May add more levels in the future.