Add variable conditional relations in workflow definition including smaller and greater than

[lfse-slafleur]

So the frontend knows to check that start_time < end_time for the simulator params_dict.

[MarkTNO]

A related issue: in jsonforms there is, next to 'minimum' and 'maximum' ('formatMinimum' and 'formatMaximum' for date), also 'exclusiveMinimum' and 'exclusiveMaximum' ('formatExclusiveMinimum' and 'formatExclusiveMaximum' for date).
We should also distinguish between greater and greater than.