Output format

[eike-fokken]

The output format I would like to have, is this one:

{
    "Componentname": {
        "var_names":[
            "name1",
            "name2",
            "name3"
        ],
        "components":[
            {
                "data_as_we_know_it":{}
            }
        ]
    }
}

The varnames are "per interpolation point"
In this way we have a unified format between one-point components like powernodes and variable-number-of-points components like the gas edges.

This would also simplify setting up general pde components, see #195