Jupyter_viz: Allow measures to be None

[EwoutH]

Currently measures crashed when it's None (which is the default). The only way to circumvent this is adding [], but that's non-ideal and not obvious.

This PR fixes that, so that measures can actually be the default value of None.

This also proves we need to test Jupyter viz in notebooks, not only in console, since both have different code paths.

[github-actions]

Performance benchmarks:

Model	Size	Init time [95% CI]	Run time [95% CI]
Schelling	small	🔵 +1.5% [+1.2%, +1.8%]	🔵 +0.6% [+0.3%, +0.8%]
Schelling	large	🔵 +1.4% [+0.7%, +2.1%]	🔵 +0.5% [-0.8%, +2.0%]
WolfSheep	small	🔵 +0.7% [-0.0%, +1.5%]	🔵 -0.3% [-0.6%, -0.0%]
WolfSheep	large	🔵 +0.3% [-0.1%, +0.8%]	🔵 -0.7% [-1.9%, +0.7%]
BoidFlockers	small	🔴 +4.4% [+3.6%, +5.2%]	🔵 +2.1% [+1.3%, +2.8%]
BoidFlockers	large	🔵 +3.5% [+2.4%, +4.5%]	🔵 +0.5% [+0.0%, +0.9%]

[EwoutH]

Thanks for merging!