Various changes, e.g. remove BoundingBox#crn

Deprecated BoundingBox#getCorners() and changed it to lazy initialization. This reduces the footprint of the BoundingBox class which is regularly used quite often (e.g. users add a BoundingBox member to each ModelInstance, in which case having a Vector3 array for every instance is just bloating). Ultimately a bounding box only has to contain its minimum and maximum values, perhaps we can eventually remove the other vectors.

Added getCornerXYZ methods as alternative for the getCorners method, as well as some other convenient method (getWidth, getCenterX, etc.).

Deprecated methods that returned a vector3 member and added an alternative to specify the vector to receive the result.