WIP: Silence py34

@almarklein can you try this branch and see if the warnings are gone on your end? Works for me on Windows. WIP because I'm not particularly happy with this solution, but we might need to use it.
This is the change that actually fixes the issue. The rest of the changes were cleanups I made while trying to solve the problem. Basically, trying to import the `ipynb` backends causes an `import IPython` to be done, which leads to the slew of warnings -- so the bug is at their end. Let me know if this does indeed solve it for you @almarklein...