Make notebook order clear

[IanHawke]

Linked to openjournals/jose-reviews#61 .

At the moment there are effectively two reading orders; the one from the front page of the static blog, and the one in the table of contents.

The front page of the blog can't be the right order, as "Part 2" often comes before "Part 1" (this is particularly clear in the Prereqs section). The table of contents is a lot clearer on this, but isn't referred to anywhere.

I would suggest putting an index.ipynb at the top level mirroring the content of the table of contents and see if there's a way of generating the static front page from that. This is, in part, because (combined with the environment) it may be possible to run the site through https://mybinder.org as an alternative to JuliaBox.

Either way, the order needs to be clearer and linked from the README as well as fixed on the blog front page.

[albi3ro]

So I have grouped the posts into series that should be read into a particular order. For the notebooks, I have a TableofContents.ipynb file that lists these out, as well as the links within each particular notebook that exists within a series.

I have now also added this functionality to the website as well.