Updating requirements.txt with all dependencies

[jasonyzhang]

[ ] Wrote test for feature
[ x ] Added changes in the Changelog section in README.md
[ x ] Bumped version number (delete if unneeded)

Changes proposed:
Added all dependencies for datascience so that pip install -r requirements.txt works for new envs.

[coveralls]

Coverage remained the same at 74.688% when pulling 3b1966c on jasonyzhang:master into 5eaeb4e on data-8:master.

[papajohn]

For now, datascience is a module used primarily by newcomers, and due to pip defaults, fully declaring the dependencies of datascience has caused newcomers to pip various problems. E.g., attempting to upgrade datascience often leads one to accidentally upgrade matplotlib and scipy. For this reason, we leave out the dependencies that are part of a standard Anaconda build.

I do agree that the dependencies should be listed somewhere, though perhaps not in the requirements.txt file.

[davidwagner]

Closing as won't-merge per papjohn's comments above.