Finished all required work

Added all vehicles and buttons for those vehicles.  Now you can create
tons of objects to put on your bridge at once and see how it holds up.
Also added drawing of all bridges via OpenGL with no textures.  I feel
like that's quite an accomplishment.  I also added loading max bridge
weight from a text file so that I can edit it if I get time to work on
this at school if I deem it necessary.  The code can't be changed at
school because I can't compile it there I think.  I'll probably add some
unneeded code in the future just to improve this, but the required work
is done!