Add research lab planets and research points (#63)

VesselUpgradeDefinition.gd

@@ -9,3 +9,7 @@ extends Resource
 @export var icon: int
 @export var additive_modifiers: Dictionary = {}
 @export var multiplicative_modifiers: Dictionary = {}
+# #63: spent from GameState.research_points per level bought, alongside
+# base_cost (ore) rather than instead of it. 0 (the default) means this
+# level needs no research points at all.
+@export var research_point_cost: int = 0