change name of directory notebook to notebook_tutorials

[jpolton]

In COAsT:example_scripts/notebooks

This is where all the notebooks live that get rendered on the docsy site.
They are all the tutorials.

They are a "don't touch unless you know what you are doing" part of this folder.

"notebooks" --> "notebooks_tutorials" might better signify that importance of these entries

[roje-bodc]

British-Oceanographic-Data-Centre/COAsT-site#89

[roje-bodc]

#630

[roje-bodc]

Changes merged into coast site repo. Just need to merge changes into the coast repo now.

[roje-bodc]

The coast side of this ticket is in develop.
The coast-site side is merged all the way through to master.