Added tuning_curves notebook

This helped me understand how to use the tuning_curves
and response_curves functions. Guessing it will be useful
to others as well!
Removed tuning_curve_1d function

And just adding a bit of special-case code for 1D ensembles in
the tuning_curve function. I think this is nicer from the user
perspective, though the special casing for 1D makes the function
slightly less readable.
Fix unit test failures

And a few other random cleanup things