(Re)implement a function that only needs the unit operation ID and type to create a unit operation

[jbreue16]

Streamlining the DG interface (#152 ), we disabled the createUnitOperation function that read the unit operation type from a strong to create a unit operation.
Right now, this function requires a parameter provider as input to construct a FV or DG unit.
As this is still a useful library function, we need to think of a solution that allows an interface without a parameter provider.