It was a bit short-sighted to combine the tag and attribute names into
one string when the Inspector requests a context menu. We will want both
values for some context menu actions. Send both names, as well as the
attribute value, when requesting the context menu.
This is in the spirit of commit a4692a6c978a6e66d171e003063449790a6c5879
(and the history behind that commit).
We will need to perform lookups from an integral node ID to the JSON for
that node frequently in the Inspector. We will also need to traverse the
DOM tree from a node, through its ancestors, to the root node. These are
essentially the same maps stored by the Qt Inspector widget.
This commit includes only fetching the DOM tree from the WebContent
process and displaying it in an NSOutlineView. The displayed tree
includes some basic styling (e.g. colors).
