Bugfix of3 d primitives resolutions

Fixes #2941. And is in response to https://github.com/openframeworks/openFrameworks/pull/3093#issuecomment-49841874.

Recalculated the vertex and index strides for of3DPrimitives so the setColor and getMesh functions for ofConePrimitive, ofBoxPrimitive and ofCylinderPrimitive work as expected.