Camera enhancements - 3rd person view etc

[Cervator]

We've needed this for quite a while and actually had it to a degree in the past with #196 - but that broke long ago. On the Alpha list of items is an entry for also converting Camera to a component approach.

A toggle for switching to a 3rd person view would be covered by this, possibly also alternatives.

We had a special "slicing" view in a contributor branch long ago, that would render as of a certain block level, cutting everything above out, leaving solid blocks as darkness. Not sure where that went but it was never finished to my knowledge.

One note: this could work without a player model but would be kinda weird. Might be nice to at least add in a placeholder like the guard model or the usual monkey head.