Fix behaviour of BoxClipper3D

[mvieth]

The constructor (as well as the setTransformation function) that takes a rotation, translation, and scaling as input, says in the documentation that theses transformations are applied to the box. But actually they are applied to the points. This commit changes the behaviour of the code to match the documentation. I considered changing the documentation to match the behaviour of the code, but

• in my opinion it is useful to have a constructor/function to describe the box (rotation, box center, box dimensions)
• the current code (which applies first scaling, then rotation, then translation to the points) is not very useful or intuitive. Imagine for example a box, one side twice as long as the others, and rotated by 45 degrees around some axis. Then it is impossible to find a scaling transformation and rotation to transform all points inside the box to the interval [-1; +1]³, considering the scaling is applied first and in each axis separately. It would always result in a parallelepiped.
• if one specifically wants to rotate/translate/whatever the points, it is easy to do so by using the constructor/function that takes an Affine3f and construct for example Eigen::Affine3f transform = Eigen::Translation3f(...) * Eigen::AngleAxisf(..., Eigen::Vector3f(...).normalized());

This also fixes incorrect references to a unit cube, which is a cube with edge length 1, or sometimes specifically a cube in the interval [0; 1]. However, BoxClipper3D uses a cube in the interval [-1; +1] (edge length 2).

Fixes #3914