GeppettoGraphVisualization requiring number as id for nodes, should be any

https://github.com/MetaCell/geppetto-meta/blob/release/v1.0.0/geppetto.js/geppetto-ui/src/graph-visualization/Graph.js#L402

I don't see any reasons for this to be a number. We usually want there instance ids, which are strings instead.
We are getting an error on console when using strings atm.

Start at geppetto.js/geppetto-ui/src/graph-visualization/Graph.js around line 402, where node IDs are handled. Reproduce the console error with a string instance ID and inspect the current number requirement. Done means graph nodes accept string IDs without the reported error; verify the existing graph-visualization behavior afterward.

Written by the indexing model from the issue text.