Add microcarrier rotational freedom

[JaroCamphuijsen]

Currently each microcarrier's orientation (or actually the locations of the cells on the microcarriers) is constantly facing in one direction, while in reality microcarriers can (and will) freely rotate due to forces of the fluid. This behaviour should be implemented, however for these we need to understand the forces on each part of the microcarrier and how they translate in a rotation (so also, how much damping will occur, etc.).
This is a pretty big undertaking and as we are considering to represent microcarriers as spheres without cells, this issue might be solved by that.