Provide a camera command line argument for headless mode

There's not an easy way to select between the camera presets/templates currently, it would be useful to specify `-camera`.

It would be helpful to provide a string version `-camera-name` (likely alias `-camera` as well, this would probably the usual use-case) and a `-camera-index`, as it would be nice to easily script a for loop to run through the cameras in your scene

Start at Chunky's command-line argument parsing and the code that selects camera presets or templates. Trace how headless rendering receives camera configuration, then verify that camera name and index arguments can select cameras and support scripted runs through a scene.

Written by the indexing model from the issue text.