Lens to support collapse/expand all

[lambcode]

The original zipkin ui has buttons to collapse or expand all nodes. Collapsing all nodes can be especially helpful to drill down into problematic issues on large traces. At the very least I think this feature should be included in zipkin-lens.

Original UI:

While we're on the topic though, I think an even cooler feature would be to collapse/expand all nodes under a specific node in the tree. Perhaps this could be accomplished from a context menu when right clicking on the current +/- button next to a span?