Carefully import extra dependencies of the example scripts

[franknoe]

e.g. seaborn. And raise a humanly-understandable error if it fails.

[jchodera]

You'll have to say something explicit, like giving the user specific instructions of what to type in the terminal to install seaborn (conda install seaborn) if you want to go this route. If we also make this pip installable, you will also have to give pip instructions.

I still think this is the wrong choice, though.