[Extension] Rework expand/collapse button

The "expand all" icon expands all apphosts and their nodes.
The "collapse" button is only available on an apphost

@adamint said to me:

> yeah, i'd like to get rid of collapse all apphosts
and turn the expand apphost resources button into a contextual expand all/collapse all resources context menu item

Start by locating the extension controls for expanding all apphosts, expanding apphost resources, and collapsing an apphost. Trace their current behavior and implement the requested contextual expand-all/collapse-all resources menu item; done means the separate collapse-all-apphosts control is removed and the resource action changes with context.

Written by the indexing model from the issue text.