Add branding header to each notebook

[jaimergp]

We might benefit from adding a standardized, custom header to each notebook to reflect the origin of the project and how to contribute back, help us develop this further and so on. I don't have any specific idea on the looks, but the Markdown cells will allow us to do anything in HTML so I think we have plenty of creative freedom there.

Some ideas:

• Star the project widget
• Add the logo
• Links to repo / documentation
• Citation instructions
• Links to other interesting software projects (ours, mainly)

[jaimergp]

CSS themes can be applied via HTML() calls on a hidden cell. Examples:

• https://nbviewer.jupyter.org/github/barbagroup/AeroPython/blob/master/lessons/01_Lesson01_sourceSink.ipynb
• https://nbviewer.jupyter.org/github/ketch/HyperPython/blob/master/Lesson_02_Traffic.ipynb