Better entity collision mask options

[KiNg626]

Currently the only control over entity collision that we have is defining the layers the entity is blacklisted from colliding with. Adding the ability to have layers that are either whitelisted (don't collide even if they share a blacklisted layer), or required (most be placed such that it's colliding with an entity with that layer) would allow for much greater flexibility in controlling where entities can be placed, and would more closely match the collisions we already have for tiles.

[Stringweasel]

+1

SE also has a few cases where this would be useful. It would be great if mods could more ways to provide the "cannot build here" player feedback.