Enhancements to stumpwimple's biplane

At the scale and resolution I was printing, the struts and part of the vertical stabilizer dropped out. My eight-year-old son was satisfied with the result, but I wanted to improve it... . I pulled stumpwimple's nice biplane STL into OpenSCAD and imposed some changes on top of it: a simplified strut configuration for printing at lower resolution, and I also added landing gear. Ben, I hope you don't mind! It looks as though you had a specific prototype in mind, and I've mundged a couple of diff