Airplane, Attempt at Ground

Drew in Airplane and airplane class but doesn't do anything except go
back and forth, calc'ed proportion of ground to background, but don't
know how to use to get dynamic ground height so hard coded, but have two
values for when you go between 1920/1080 and regular screen dimensions,
all based on .5 zoom
Merge pull request #6 from slowben/Ben

Airplane, Attempt at Ground