Gallery of Examples

We could move to a gallery of examples, upgrading a few of them as we go. By default this means that they are a bit harder to interact with from the package (i.e. they are more part of the docs than the code). But I think we can get away with that by doing a make script etc.

Things:

• Better visibility on examples
• Can download them individually as .ipynb or as .py
• Captures output
• Need to copy from package to docs
• Would like to introduce properties into some of the examples to help document them.
• Need to think about how to show examples from sub packages.

[rowanc1]

Some progress:

[lheagy]

closed with #570, #557 http://docs.simpeg.xyz/content/examples/index.html