Update the Solar System notebook for Skyfield 0.1

And, enable inline screenshots for the iPython Notebook viewer.
Add text to the 3D Solar System notebook
Make space behind the Solar System black
Add screen captures to Solar System notebook

This will let people view it online through the IPython Notebook Viewer
and see an example of the resulting 3D window, to give them a better
idea of whether they are interested in trying out the notebook live on
their own system.
Switch 3D Earth Satellites to Skyfield

Wow, the interface is still very clunky, but even with Skyfield 0.1 it
is now possible to get Earth-satellite positions directly from its
interface instead of having to make raw calls to the sgp4 library.
Switch to precomputing satellite positions

Otherwise the animation runs too slowly. Also, fixes #8.
Add inline images to 3D satellite notebook
Merge branch 'master' into jep-dev-dev