removing optional dependencies

[basnijholt]

(original issue on GitLab)

opened by Anton Akhmerov (@anton-akhmerov) at 2017-11-27T12:30:10.501Z

Looking at the requirements, we really only need scipy and sortedcontainers (numpy is a dependency of scipy already).

The rest (holoviews, ipython, ipyparallel, distributed) shouldn't be required.
To make all these optional, we can enclose all corresponding imports into try-catch.

[basnijholt]

originally posted by Anton Akhmerov (@anton-akhmerov) at 2017-11-27T12:31:04.920Z on GitLab

Then of course we'd need to create mock versions of the corresponding executors, or add extra try-catch statements in the checks.