Fix #406. EGP polys draw on correct side of screen

EGP's Poly object now uses render.CullMode to draw clockwise vertices.
The E2 functions egpTriangle and egpTriangleOutline now use Poly and
PolyOutline.
Merge pull request #415 from wiremod/bidirectional-polygon

Fix #406. EGP polys draw on correct side of screen