Include output variables for "submodel" when that submodel it is active

[Peter9192]

For example: when radiation switch is on, then radiation variables/parameters(?) must be included in output.

[Peter9192]

Relates to #94

[sverhoeven]

Part of #104

[Peter9192]

#144 makes unset vars default to 999, so you always have a complete output set but it is clear that these parameters are unused by the model in the current run.