S7 naming conventions

[JosiahParry]

Related to #453

I am working on implementing S7 classes for arcgisutils and one thing I'm not quite sure on is how to handle the naming convention for S7 classes.

S7 exports classes with the prefix class_. Is it recommended that R packages that export S7 classes export it with the struct class_{class_name}?

[t-kalinowski]

My understanding is that the class_ prefix is only for base S3 class proxies. For all other classes, we've adopted a convention of using CamelCase (more precisely, PascalCase) for the class name (which is also the name of the constructor).

This reminds me, I think it would be good to revisit #461 for the next release.