Enable the script editor line length guideline by default

[Calinou]

Now that the GDScript style guide has an official recommendation, it makes sense to enable the line length guideline by default.

[akien-mga]

I still feel 80 chars is way too low on today's high resolution 16:9 monitors (compared to the old 4:3 in 800x600 or less in use back when this convention was adopted for code), but let's give it a spin and see what people think of it :)

[Calinou]

@akien-mga We could move the default guideline position to 100 characters eventually. I didn't think about doing it right away, as the "soft limit" in the style guide is currently 80 characters.