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/ra/maps/desert-shellmap/rules.yaml

@@ -3,6 +3,10 @@ Player:
 	LobbyPrerequisiteCheckbox@GLOBALBOUNTY:
 		Enabled: False
 		Locked: True
+	PlayerResources:
+		ResourceValues:
+			Ore: 0
+			Gems: 0
 
 World:
 	-CrateSpawner:
@@ -12,8 +16,6 @@ World:
 		BackgroundMusic: intro
 		AllowMuteBackgroundMusic: true
 		DisableWorldSounds: true
-	ResourceType@ore:
-		ValuePerUnit: 0
 	LuaScript:
 		Scripts: desert-shellmap.lua
 	-StartGameNotification: