Cleanup examples

[ianthetechie]

This cleans up a few specific issues I noticed while doing a quick review of the previews:

• The camera demo was broken, because the default (unreleased) behavior of the new environment modifier is to disable the camera ;) See mapCameraDisabled defaults to true? #128. I suspect this was accidental as a result of indecision on how to name it. I renamed the file to reflect how the modifier currently works.
• Add an explicit constant camera to a few of the examples that didn't set a camera before. Some default somewhere changed so that these no longer defaulted to a useful viewport, so I've fixed that.
• Removes some stray props that were not used and distract from the unsafe modifier example.

Fixes #128.