Add overwrite functionality

[KANAjetzt]

Let mod authors create the overwrites.gd at the root of the mod folder

• My current proposed solution on how to handle the overwrites
• Mod authors create the overwrites.gd script and overwrites folder in there mod folder:
  
• We provide tooling to make the creation of the overwrites.gd script a one click thing
  • Tooling will be developed in the Mod Tools Repo
• People ho don't want to use extra tooling can just write the overwrites.gd them self

overwrites.gd from example mod:

extends Node

func _init():
	var overwrite_0 = preload("res://mods-unpacked/KANA-OverwritesTest/overwrites/assets/images/GodotModded.png")
	overwrite_0.take_over_path("res://assets/images/GodotModded.png")

Example Mod with this setup:
KANA-OverwritesTest.zip

Testing Godot Project
( does not include the Mod Loader - pls use this PR to test )
ModdingTest.zip

closes #14

[ithinkandicode]

Just some very minor things, borderline nitpicks 😁

[ithinkandicode]

Could these funcs be renamed into something more semantic, ie. to be more human readable? The phrase "is file existing" isn't quite grammatically correct. Eg. would does_file_exist be ok for you?

[KANAjetzt]

Maybe just use the build in function name?
file_exists

[ithinkandicode]

Lookin' good man! Looks like I'll need to re-approve once the merge conflicts are fixed but I'll approve here anyway 😁