Expose near & far clipping distances

[ghost]

The near clipping and far clipping distance is not working. I think blenderseed is not exporting that data to the appleseed scene.

[jdent02]

There is no far clipping distance for the appleseed camera and the near clip (called Near Z in appleseed) is currently not exposed. We're making a lot of changes to the exporter so expect this feature to be supported soon.

[dictoon]

A far clipping plane has been asked multiple times, it's time we at least create a ticket to track this feature so here we go: https://github.com/appleseedhq/appleseed/issues/1770

[jdent02]

Near clip has been exposed with #126