Based on the 2D Beginner Project look, these demos now have the colorful
GDQuest "theme" to them.
This had the effect of removing the circle and triangle/ship sprites as
everything is drawn in Godot directly.
Used `var variable := 0.0` as discussed in the Godot issue, instead of
`var variable: = 0.0`.
Mostly these are minor/cosmetic changes, but I've also reorganized the
folder structure (naming of folders) to reflect our guidelines, plus
made some minor changes to the demo codes. Still work in progress.
Changed text boxes to sliders to improve usability. This also involved
adding some simple graphics, since the _draw method is not
anti-aliased and doesn't look great.
