Create Jupyter version of example 6

[dtabell]

Tasks for this example:

• start with Oleg‘s python script for example 6
• convert intro to MD
• crib iron-dom. text from example 5
• update imports
• delete __name__ guard and divide code into coherent cells
• add 3D widget
• add appropriate arguments and comments to create quad function
• update plots
• add explanatory text and headings
• verify and test harmonic analysis
• query Oleg re factor of 4 in sizeof(Intxn Mx)
• add illustration (.png) for this example