fix(python): fix Python3 jupyter deadlock issue
fix(python): fix Python3 jupyter deadlock issue

Previously, on Python3 with Jupyter notebook server 6, Neuroglancer would share an existing asyncio
event loop created by Jupyter, which meant that the Neuroglancer webserver would be unable to
respond to messages while a cell evaluation was in progress.

Fixes #170

google/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer,google/neuroglancer,google/neuroglancer