visualization of eigenvectors and edge flows

[cookbook-ms]

Usually we want to visualize not just one eigenvector but a set of them, so in this case, it is better to use a unified colormap for all of them.

A few points:

• all the text labels, if they are mathematical symbols, let's use latex
• the current labels on the nodes and colormap are too small
• also, if we want to show the gradient eigenvectors, it is better to indicate the corresponding node values which result in the eigenvectors, which is why we need to the colormap for node values too
• if we want to show the curl eigenvectors, it is better to indicate the corresponding triangle values which result in the eigenvectors

[cookbook-ms]

when computing or returning the eigenvalues and eigenvectors, it's recommended to order them based on the magnitudes of the eigenvalues, e.g., from small to large

[irtazahashmi]

when computing or returning the eigenvalues and eigenvectors, it's recommended to order them based on the magnitudes of the eigenvalues, e.g., from small to large

I have fixed that.