Tim Lüttmer

In the (proposed) addition of terminal velocity attribute for ice particles, approximation_liquid and approximation_ice conflict. The terminal velocity attribute of ice particles (signed_mass < 0) is falsely overwritten by terminal...

Currently the function names are unclear. Rename them to be consistent with references of the respective parametrisation (like gunn_and_kinzer, rogers_and_yau) https://github.com/open-atmos/PySDM/blob/9fe8433af528ed0909b561abbb6c67632df96463/PySDM/backends/impl_numba/methods/terminal_velocity_methods.py#L12

Implement parametrisation for general functional relationship between reynolds number and drag coefficient of solid (ice) spheres.