Possible changes for v0.17

[lmdiazangulo]

• Change the strings that are used for vectors, e.g.

  core/testData/dmcwf/dmcwf.smb.json

  Lines 7 to 11 in 15a852a

  	"gridType": "gridCondition",
  	"type": "Number_of_cells",
  	"numberOfCells": "{20 20 20}",
  	"layerBox": "{0.012000000000002719 0.012 0.192 -0.0 -2.693855815499857e-10 -0.03}"
  	}

  to something more compliant with json such arrays. The string format is basically inherited from previous limitations with GiD and it is not very comprehensive in some cases.
• Sources and Probes typically refer to elemIds which are in the mesh structure. Until now, a .smb.json contained only a single unstructured problem description (as in: https://github.com/OpenSEMBA/core/blob/main/src/core/ProblemDescription.h) , but maybe we will have to extend it for: StructuredProblemDescription and MTLN cases... It is worth to give a thought to make it more coherent.