LB: Add additional clickspot/gesture for collection/tree display:

[EazyCheeze1978]

When one wants to quickly get to another main branch of the Platform/Categories tree, it can sometimes be frustrating/time-consuming to totally expand or collapse it.

So, my proposal this time is pretty minor, but it could help things out: make top-level Arrows/Triangles that indicate a collapsed (pointing right) or expanded (pointed down) view, or triangles for any category that have further categories, platforms or playlists lower in the hierarchy, instead of bringing up the Collection-adding menu upon right-click, bring up another menu with four options, Expand All in this category, Collapse All in this category, Expand All and Collapse All.