Persistent settings and code

[wmww]

We need the ability to load and save brainfuck source files. It would also be nice to keep settings and/or open file persistent across closing and reopening the IDE. I've no idea how to do this, but Godot probably makes it somewhat painless. It may or may not be a good idea to wait on #4 (Port to Godot 3) for this.

[locness3]

About loading files : https://docs.godotengine.org/en/2.1/classes/class_file.html
For keeping settings etc, I'd use user:// paths to store config to the user directory.