Add spec to check if all nodes (which have costs) are part of a cost group

[MartLubben]

New nodes with costs should always be part of one of the cost groups. Knowing that we will probably keep on adding and changing nodes, this will surely go wrong soon or later. I am not sure if it is possible, but it would be nice to have a check for completeness of the cost calculation by the mechanical turk.

Maybe it is als simple as stating that:
All nodes which do not have 'nill' costs should be part of one of the cost groups below. However I can imagine that is is more difficult.

Cost groups (couldn't select the list and made a picture) :

[DorinevanderVlies]

@mabijkerk please get in touch if you want to discuss this

[mabijkerk]

Thanks for this @DorinevanderVlies and @MartLubben. I think this is not something that should be picked up in Mechanical Turk, but in specs on ETSource. @kaskranenburgQ could you open an issue to write a spec for costs in node files on ETSource?