Add research lab planets and research points (#63)

VesselDefinition.gd

@@ -23,6 +23,10 @@ extends Resource
 @export_multiline var unlock_description: String
 @export var unlock_cost: int
 @export var unlock_resource_costs: Dictionary = {}
+# #63: spent from GameState.research_points, alongside unlock_resource_costs
+# rather than instead of it. 0 (the default) means this unlock needs no
+# research points at all.
+@export var research_point_cost: int = 0
 @export var unlock_icon: int = -1