Chai data structure should support multiple cameras

[Samir Menon]

For now, there is a clight class, but only one cam supported per graphics spec.

It's feasible to use multiple graphics specs but it would just be cleaner to support multiple cameras (this was the original plan anyway).

In a nutshell, look at SGraphicsParsed.hpp. It should have a vector of cameras. Instead it only has one.

However, this stuff is hard wired into many places and might require some long-range tweaking. Low pri.