Do not use "import *" in notebooks

[impredicative]

In Python it is considered bad practice to use from <something> import *. That's because the imported objects thne clutters the namespace, and it is not clear where the imports are coming from. This issue is manifest in the notebooks. The notebooks should be updated to use proper explicit imports, e.g. from <something> import foo, bar, etc or import <something.thing>.

@hiohiohio