Tax system

- New tax system
- Advisor window modeled after SC3k's
- Advisor start_dialogue() function is now connected to a SimEvent "advisor_message" signal
- Advisor windows are now autoloaded and no longer part of the core interface node
- Added 3D buildings from Micropolis repo

scripts/power_station.gd

@@ -0,0 +1,16 @@
+extends "res://scripts/zone.gd"
+
+func _ready():
+	SimEvents.connect("has_power", self, "_power_zones")
+
+func _power_zones():
+	SimData.power_grid += 1
+	
+	if SimData.power_grid <= 1:
+		SimData.has_power = true
+
+func _input(event):
+	_drag_drop(event)
+	
+	if can_grab == false:
+		SimEvents.emit_signal("has_power")