Showing two lists in a paned was a bit awkward, and space was
getting too limited. Go back to showing just the node list at
first, and make the CSS properties available via a stack. At
the same time, add a right-click context menu to the node list
to make the name and class editing more easily available.
When the CSS style of a node changes, we want to display the new values
in the inspector.
This for example allows to see how styles update on hover or during
animations.
strcasecmp() is unfortunately not universally available, along with
strings.h. Fix the build by replacing strcasecmp() with
g_ascii_strcasecmp(), and remove the strings.h include.
https://bugzilla.gnome.org/show_bug.cgi?id=747604
