add Screens system

[Jeremi360]

Adds "show", "hide", "at" and "with" keywords to RKScript and Screen nodes. This implements #143

[theludovyc]

Hello :)

I will not review 2761 files with +91,863 −31 updates.

Please say me the files you want I see, or merge it if you are confident :)

[Jeremi360]

Hello :)

I will not review 2761 files with +91,863 −31 updates.

Please say me the files you want I see, or merge it if you are confident :)

@theludovyc This is not ready for review/merge as it doesn't work as it should. The biggest problem I have is that I have on helper object BaseScreen.gd, so I can easy you the same code for Node2D as for Control. But for some reason it works for Node2D, but not for Control. See scripts: Screen.gd and Screen2D.gd Screens are added to Rakugo Scripting by Screens.gd singleton. There is res://game/ScreensExample.tscn scene that I use for testing Screens visually.