Do not store every coordinate of the bounding box

[bauerdavid]

Currently every corner of the BB is stored, but is actually not used (they are reduced to the minimum and maximum points). This is hard to use (to add a new bounding box, all corners have to be generated), and gives error opportunities (what happens if someone programmatically changes a single corner?)
Instead every bounding box should be provided with two corners, which can be used to get every other corner.