Fix .ipynbs to handle upsampling

[kelseymarkey]

We are now allowing both upsampling and downsampling in our workflow, so we need to update some file names in our current notebooks to reflect this.

• [x] Both upsample.ipynb and downsample.ipynb should be fixed so that they output a file called idx_train.pckl.
• [x] vectorizer-count.ipynb should be fixed so that it reads in this idx_train file (instead of downsampled_idx_train.pckl as it does currently)
• [x] concat-features.ipynb should be fixed so that it reads in this idx_train file (instead of downsampled_idx_train.pckl as it does currently).
• [x] concat-features.ipynb should be fixed so that it no longer outputs datasets in the form {dataset}_{vectorizer}_downsampled_data.pckl since this can now be upsampled data. Sid has now changed this to `{dataset}{vectorizer}_subsampleddata.pckl`.
• [ ] All modeling notebooks which call in data in the {dataset}_{vectorizer}_downsampled_data.pckl form should be corrected. (Sid- baseline models, Kelsey- NB, Aren- modeling notebook)

[kelseymarkey]

Assigning to @charlesoblack to handle second, third, and fourth points above (and update any modeling notebooks as necessary).

Assigning to @arendakessian so that he can update any modeling notebooks as necessary.

[kelseymarkey]

Tested Sid's changes to vectorizer-count.ipynb and concat-features.ipynb, all behavior as expected.

Also updated my modeling notebook (Naive_Bayes.ipynb) to reflect these new file names (commit 1526bcd1130c510ca7e5d8624a890b509869edd1).

Only remaining task is for Aren and Sid to update their respective modeling notebooks.

[guidopetri]

I want to make sure that this works before closing it but it's next in line.