Overhaul resource layer logic:

* ResourceType trait has been removed.
* Simulation-related data is now defined on the
  ResourceLayer (which mods can subclass/replace).
* Support non-money resources by moving the resource
  values to the PlayerResources trait.
* Allow mods to disable the neighbour density override
  and instead always use the map-defined densities.
* Allow mods to define their own resource placement
  logic (e.g. allow resources on slopes) by subclassing
  (Editor)ResourceLayer.
* Improve ability to subclass/override ResourceRenderer
  by exposing more virtual methods.

mods/d2k/maps/shellmap/rules.yaml

@@ -1,13 +1,14 @@
 Player:
 	-ConquestVictoryConditions:
 	-HarvesterInsurance:
+	PlayerResources:
+		ResourceValues:
+			Spice: 0
 
 World:
 	-CrateSpawner:
 	-SpawnStartingUnits:
 	-MapStartingLocations:
-	ResourceType@Spice:
-		ValuePerUnit: 0
 	ActorSpawnManager:
 		Minimum: 1
 		Maximum: 3