Only use viscosity as a field
Rigth now, the viscosity is used through its specification.
Disk::computeViscosity(this one is expected)
Disk::initRadialVelocitythis one is weird,
- the main problem here is that viscosity comes into play only starAccretion.type is not SA_WIND... how are the 2 connected ?
- but also the value of the field is used differently depending on its type
- in DiskPhysic::Viscosity::alpha the weird thing is that both the returned value and its usage depends on the type.
- in DensityTheo
This is a sub task of #544 .