* 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.
Objectives can be either primary or secondary objectives. Primary ones
influence the outcome of the game. If all primary objectives are
completed the game is won, and lost when any of them fails.
Objectives can be added at any stage during the game, allowing to react
dynamically to game events.
The objectives backend only contains the information about the
objectives themselves. It does not check if objectives are completed or
failed. Instead, the state of objectives must be manually marked. The
backend, however, does check whether the game is won or lost.
