Clear out entanglement between ImportFormat and InputSource

[dcolleoni]

ImportFormat is not InputSource. It should be properly separated. Adjust the dependent code.

snippet:

//Format
public string Format => args.ImportFormat; //remove it as a string
private IEnumerable loadPersistedInputSource => args.ImportFormat switch { //use this instead of Format in IfrsVariables (193) and adapt the logic
ImportFormats.Cashflow => (InputSource.Actual).RepeatOnce(),
ImportFormats.Actual => (InputSource.Cashflow).RepeatOnce(),
ImportFormats.DataNodeParameter => new InputSource[]{InputSource.Cashflow, InputSource.Actual},
_ => (InputSource.All).RepeatOnce(),
};