More extensible ShadowCameraSetup

[claustre]

Indeed, I used it to derive a particular behaviour for directional lights, and realized I have to rewrite many parts because it is not written as to be inherited.

For instance the PlaneOptimalShadowCameraSetup class has private members. The FocusedShadowCameraSetup has protected members but that are non virtual. So you have to rewrite getCamera() in order to have the right overloaded functions be called.

Just a matter of "protected" instead of "private" and some virtual functions as well...

[sinbad]

Perfectly open to this kind of thing, easiest thing is just to change it yourself and submit a patch..