Bug: Some steps rely too much on numpy

[guillaume-chevalier]

@alexbrillant please notice this to avoid using numpy.

It's not for no reason that there is a package neuraxle.steps.numpy for numpy steps: regular steps should NOT use numpy, or at least avoid to use it as much as possible to keep Neuraxle generic.

Describe the bug
Too many steps use numpy where they shouldn't

To Reproduce
Use a StepClonerForEachDataInput or a FlattenForEach

Expected behavior
The input data may be lists of strings or other types that are possibly incompatible with numpy or of discontinuous nested shapes

Additional context
Don't call np.array in the data containers of the handle methods.