(Study View) Cancer studies chart filter refactoring

[dippindots]

Fix cBioPortal/cbioportal# (see https://help.github.com/en/articles/closing-issues-using-keywords)

Describe changes proposed in this pull request:

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• b

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[onursumer]

For certain filter combinations the new version ends up with way more number of samples than it is supposed to.

Before (31 patients / 31 samples):

After (401 patients / 409 samples):

For some reason the new code generates a wrong filter object by including all the studies instead of the selected two only:

[alisman]

@dippindots just wanted to make sure you saw the above