Add some graphical representations on shocks

[astrojuanlu]

Examples:

[astrojuanlu]

Oblique shocks charts were already added as an example:

https://github.com/Pybonacci/scikit-aero/blob/master/examples/Oblique%20shocks%20chart.ipynb

It is worth it to

• Complete oblique shocks chart with legends of the sonic line and the maximum line

and also add handling of

• Pressure-deflection diagrams
• Graphical representation of shocks
• Intersection of shocks overloading operators on diagrams and shocks themselves