get_performance_info() - add Nodes count to output

[fireday2]

Right now the func 'get_performance_info()' from "res://addons/panku_console/modules/engine_tools/module.gd" returns three values: "FPS: %d | Mem: %.2fMB | Objs: %d"

I suggest also counting Nodes. I think it is useful information It's easy to add with 'Performance.OBJECT_NODE_COUNT'. But it counts Panku Nodes as well. That's why I created a function to calculate it in a cycle, excluding Panku Nodes.

Perhaps excluding Panku Objs from the total sum of Objs could also be beneficial.

[Ark2000]

Seems the newly introduced counter is a little time consuming, I suggest make it optional. like this, which will be more flexible and backwards compatible.

func get_performance_info(count_nodes := false) -> String

[Ark2000]

get merged in #191