Support DIC data for multiple time steps

[CsatiZoltan]

Currently, the DIC class knows about the displacement field at a given time step only. On the other hand, one is often interested in the evolution of the displacement field. It is clear that loading the displacement measurement data for each time step is not viable in general on personal computers¹. Moreover, the member functions of the class would become more verbose because the user would need to give at which time step a given operation should be applied. Since the class cannot know in advance how the series of displacement fields are stored, it is the responsibility of the user to pass it to DIC. The DIC class should have a method that loads the new field.

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¹E.g. in my current dataset, the DIC data is given as an HDF5 file with the size of 38 GB.