GEXF Legend

[mbastian]

Discuss legend specification: https://github.com/gephi/gexf/tree/legend/specs/1.3.1

[mbastian]

Great start! One minor comment to start the conversation :)

• In viz:color maybe for is better than use so it's similar to attavalue, when we refer to a column

[paulgirard]

The use attribute disappeared after we chose to nest viz-colors into the corresponding attribute.
I propose we move the discussion in the PR page.