Add jupyter notebooks

[pFernbach]

Add 3 notebooks showing basic usages of the API, how to create a Contact Sequence from scratch and how to load it from a file and use the data stored inside to plot/display the motion.

Also add a new constructor to ContactPatch that take a ContactModel as argument.

[nim65s]

Hello

I'm a bit late for the review, sorry :)

Everything looks really good, I just made tiny editions for some details.

But I have one error :

matmul: Input operand 1 has a mismatch in its core dimension 0, with gufunc signature (n?,k),(k,m?)->(n?,m?) (size 12 is different from 3)",

Could you check this ?

Also, I would advise to use the "restart kernel & run all cells" before saving a notebook, to check that everything works and have nice numbering of the cells ;)