* 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.
* Rename LeftColor and RightColor to MinColor and MaxColor
These are mapped from LowRadarColor and HighRadarColor in
the original inis, and appear to be used to set the bounding
values for selecting a random colour, NOT for left/right
pixels (which caused noticeably wrong banding).
* Adjust brightness based on terrain height.
MinHeightColorBrightness and MaxHeightColorBrightness
were chosen by trial/error to match the original
map preview rendering.
