feat(data-manager): Added a data manager class

[talolard]

Per #80 made a DataManager class. Probably easiest to get a sense of it through the examples, but highlight is that users don't need to do bookeeping because they can just do

        for ix in indices_to_label:
            original_ix = manager.get_original_index_from_unlabeled_index(ix)
            y = original_labels_train[original_ix]
            label = (ix, y)
            labels.append(label)
        manager.add_labels(labels)
        # clear_output()
    learner.teach(manager.labeled, manager.labels)

And the manager keeps everything in sync.

I bet the API can be improved, but it's a solid and convenient start. Looking forward to feedback

[cosmic-cortex]

@talolard Hi! I am really sorry, but I forgot to review the PR :( In the last month I was working crazy hard to launch a new startup and a new product, so I set everything aside. If it is still fine by you, I'll review it now and add it.

[codecov-io]

Codecov Report

Merging #81 (3281990) into dev (1e23453) will not change coverage. The diff coverage is n/a.

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##              dev      #81   +/-   ##
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  Coverage   97.19%   97.19%           
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  Files          31       31           
  Lines        1641     1641           
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  Hits         1595     1595           
  Misses         46       46           

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