Add operator to convert 2D projection matrix into 3D view point

[glopesdev]

Currently drawing 3D objects requires a specialized structure containing the view matrix, projection matrix and light source for rendering the scene. It would be useful to include a node for converting 2D (or 3D) projection matrices straight into a fixed 3D view point e.g. (Eye at (0,0,0) looking into -Z) and fixed or configurable light source.

This would allow easily drawing 3D objects into the eye-centric coordinate frame which is very useful in certain situations.