Add SVG restyle to match vscode theme

[jotavemonte]

Summary

Intercept the SVG generated by graphviz and change the colors according to the vscode current theme.

Address the #24 "Make graph nicer." milestone

How it works

Explore the graph using a BFF algorithm, for each node, change the children's values according to their classes.

Evidences

[jotavemonte]

@beicause I used the selection background color for the nodes and it isn't ideal in every theme, but in most of them it looks good.

[beicause]

I think we'd better to theme the graphviz( .dot ) file directly. Changing the style of svg doesn't affect the .dot file we save.

[jotavemonte]

@beicause Sure! Should we have this as a temporary solution and then I can open an issue to migrate the solution to the other end of the file generation? With this strategy, we would have themes for the graphs right away.

[beicause]

I have no reason to merge this PR now which adds unnecessary complexity if there is a better approach. Let's improve it firstly.

[jotavemonte]

@beicause I was investigating the options and AFAIK that the color palette is only available at the web view step - we could use some placeholders and interpolate them, but this would add some complexity and processing to the rendering step too.

Do you have an idea on how to approach this? Thank you.

Edit: My previous assumptions were incorrect.