## WIP: New Evap-Cond Lagrangian model (FuchsKnudsen) for solution (liquid + solid) droplets

Adding evap-cond Lagrangian model for solution droplets

```
1) Adding LiquidEvapFuchsKnudsen model for Lagrangian evaporation.
This models is based on a diffusion type of evaporation/
condensation on particles composed of solution (liquid + solid).
2) Adding modes of calculating the particle rho and volume change.
The new keyword in constantProperties is volumeUpdateMethod
which three options:
a) constantRho
b) constantVolume
c) updateRhoAndVol
3) The entry rho0 is now optional for multicomponent parcels.
If defined , it is used but if it is not the actuall mixture
provided is used to calculate rho0 of the particle
T0 is still used as initial T and Cp0 is over-written in the
multi-component cloud
```