Travis should run the demo notebooks as system tests, and deploy the rendered versions as supporting documentation

[drphilmarshall]

Here's the to-do-list:

• Make travis run our demo notebooks, following the example in SLTimer
• Have travis deploy the rendered versions to an orphan rendered branch, in the same way that beavis-ci does.
• Make the API docs point at the rendered notebooks.

The problem is that the notebooks exist in the issue/17/desc-note branch, while the API docs are also not yet merged. I suggest we do the first two items in a sub-branch off of issue/17/desc-note, while getting the API docs merged into master in parallel. Then we can pull in the API docs to the Note branch too.

[jiwoncpark]

Correction: the demo notebooks are in all the branches, not just the issue/17/desc-note branch, so we will branch off of master (issue/50/notebooks-ci) to fix this issue. The point about getting issue/43/api-docs merged into master in parallel stands. Once both branches are merged, we can have the API docs point at the rendered notebooks.

Currently, the demo notebooks are hiding in slrealizer/demo so we'll make them more visible by bring them to doc while flattening doc/notebooks and doc/tutorials.