SoilDyn: Misleading console message

[RBergua]

Bug description
SoilDyn includes two available CalcOptions at the moment:
Calculation option {1: Stiffness / Damping matrices, 2: P-Y curves [unavailable], 3: coupled REDWIN DLL}

Currently, as soon as SoilDyn is being called, a message in the console is written down:
SoilDyn returning only non-linear portion of reaction forces

However, this may be slightly misleading for the users because non-linear forces are only computed and send from SoilDyn to SubDyn if REDWIN (CalcOption = 3) is used.

CalcOption: 1 uses a linear stiffness matrix. This is equivalent to use SSI in SubDyn directly.

CalcOption: 3 uses a linear stiffness matrix AND non-linear forces computed by REDWIN are applied to SubDyn.

I believe it would be better to display the message about non-linear forces only when REDWIN is used. I'm fixing some bugs and will address this message there as well. I will open a PR soon.

[jjonkman]

Perhaps change the message to state that the linear portion of the stiffness is sent directly to SubDyn as a stiffness matrix, rather than as a load, and other terms are transferred as loads. Such a message would apply to all CalcOptions of SoilDyn and it is the stiffness matrix transfer that that is "special" compared to other module couplings within OpenFAST.

Best regards,