Sankey Enhancements

[pborissow]

• Provide hints when tree is out of balance
• Ensure support of multiple distributors
• Allow users to set/update title
• Ensure node names are unique

[smurff]

To make the Sankey useful, we will want the ability to show values within the distribution points. At first, they should be manual.

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• Eventually, we want the ability to allow for a user to assign an API endpoint.
• We likely may want to also allow for "Add value", which creates a new field + value pair.