redundant attributes in calss `Variable` for create_fmu_container

[jbernalr]

it seems to me that there is some redundancy in the class Variable in the module create_fmu_container.

It is not possible to create a fmu container if the fields in Variable, for instance type are not filled in. Yet, in mapping one defines a unique correspondence between a variable in a specific fmu of the container.

The information: type, variability, causality and name should be inferred/read automatically from mapping as in any case it is not possible to remap this information. i.e. its not possible to make an output a parameter or the like.

Notice that in previous versions of create_container_fmu this was not necessary.