Check and fix units rainfall erosion sediment

[vers-w]

1. soil_erosion__eurosem_exponent has a default value of 2.0. However in the original equation (that uses a default value of 2.0) for soil detachment by raindrop impact this parameter has unit $\mathrm{mm}^{ -1}$ (multiplied by water depth [mm]), and in Wflow the unit of water depth is in [m]. This needs fixing in the release/v1.0 branch and will be fixed in Use SI units for internal computations #735.

2. The multiplication with 0.001 below in the function rainfall_erosion_eurosem is not required based on the units:

   #Total kinetic energy by rainfall [J/m2]
   ketot = (rddir * kedir + rdleaf * keleaf) * 0.001
   

   This also needs fixing in the release/v1.0 branch and will be fixed in Use SI units for internal computations #735.

3. Based on the first point, the soil erosion for EUROSEM is now much higher compared to ANSWERS (function rainfall_erosion_answers). Need to check if units for the ANSWERS parameters are correct, especially the usle_k parameter that is now provided in metric units.