Hide move a panel up/down

[taramk]

This feature needs a little work to feel polished, and I'd like to know if it's something people need before we spend time on it. It has prominent placement in the UI so we should be sure it's earned that spot. The side-by-side view works well and I'd like to see if that solves this need for now.

Some issues:

• no way to revert to side-by-side view
• very large margins between top and bottom panel (need to decide how big to make each panel—fit contents? scroll?)
• if left/top node is large, it's unclear that a node has been moved below (need better visual feedback)

[taramk]

@progrium - let me know what you think