I would like to be able to enhance an outline with a 'category'
on labels so that an outline might appear as:
with the ... provided by a standard label provider and the
<then> provided by a prefix.
A plausible approach might be to create a PrefixedModelTreeNode.
However this is a bit klunky since new ModelTreeNode occurs in many
places; factoring creation into a createTreeItem() would help.
A derived ModelTreeNode is actually impossible since nodes are
maintained in an array rather than a list. Gioven the use of an
arraycopy for each addition it is far from clear that the array
gives a performance benefit.
So perhaps the category integer could be annexed by creating an
integer-to-prefix string map; but who else uses categories, so
how can the category integers avoid conflict?