terminal velocity of ice particles

[tluettm]

TODOs:

• [ ] change dependency settings for terminal velocity of ice
• [ ] refactor names of methods in terminal velocity backend for clarity
• [ ] check if (more) unit tests for particle displacement need to be changed to test displacment of ice particles
• [ ] Solve problem: terminal velocity of liquid particles overwrites terminal velocity of ice particles. Hence order of function call matters.
• [ ] implement parameterisation for drag coefficient of smooth spheres for intermediate and large reynold numbers