125 merge substrate classes from pld and movpe and place it under ikz category

[aalbino2]

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[aalbino2]

I'm basically done. I tried the following solution at the beginning for the SubstratePreparation class:

class SubstratePreparationStep(Activity):
    m_def = Section()

class EtchingForSubstrate(SubstratePreparationStep, Etching):
    pass

It was not convenient because we would have seen twice each Activity listed in the IKZ category, e. g., EtchingForSubstrate and Etching.

So I went for the solution in which we have SubstratePreparationStep class in basesection.py and we stick it to whatever class will be needed into a SubstratePreparation

[aalbino2]

@ka-sarthak I think when solving the #126 you could place the XRD stuff in the new characterization submodule here in IKZ_plugin