add memory usage module with collector, scene, and script

scenes/dashboard.gd

@@ -27,6 +27,10 @@ func _add_modules() -> void:
 	grid.place_module(cpu, 0, 0)
 	_modules.append(cpu)
 
+	var mem := preload("res://panels/memory/memory_module.tscn").instantiate()
+	grid.place_module(mem, 1, 0)
+	_modules.append(mem)
+
 	var timer := Timer.new()
 	timer.timeout.connect(_refresh_modules)
 	timer.autostart = true