Currently it's a bit of a mess, since

- prioritized tile has a ptr to a tiling and a tile
- but tile also has a ptr to a tiling
- tile also stores some state on it that is accessible from tiling.

tile manager happily accesses all three places in different spots.

It's very confusing and it's unclear 
1. where to find some data that tile manager has and
2. where to add new data.

We need to clean this up.