[Highcharts-3D] Improved algorithm to select visible faces when drawing cuboids

The current code compares 2 vertexes' X or Y positions to decide if each face is visible or not. This simple approach works fine for small rotations, but causes glitches on larger angles.

The new approach calculates each face's area to verify if it is front-facing (negative area, CCW vertexes) or back-facing (positive area, CW vertexes) and returns only the front-facing paths.

Reproduction: http://jsfiddle.net/hxmw8y9s/2/