material dialog
===============
Usage: material.showDialog(<path>, [<title>], [<x>], [<y>]);
the path should point to a property "directory" (usually set in
the aircraft's *-set.xml file) that contains any of
(shininess|transparency|texture) and (diffuse|ambient|specular|emission),
whereby the latter four are directories containing any of
(red|green|blue|factor|offset).
If <title> is omitted or nil, then the last path component is used as title.
If <x> and <y> are undefined, then the dialog is centered.
Example:
<foo>
<diffuse>
<red>1.0</red>
<green>0.5</green>
<blue>0.5</blue>
</diffuse>
<transparency>0.5</transparency>
<texture>bar.rgb</texture>
</foo>
material.showDialog("/sim/model/foo/", "FOO");
Of course, these properties are only used if a "material" animation
references them via <*-prop> definition.
Example:
<animation>
<type>material</type>
<object-name>foo</object-name>
<property-base>/sim/model/foo</property-base>
<diffuse>
<red-prop>diffuse/red</red-prop>
<green-prop>diffuse/green</green-prop>
<blue-prop>diffuse/blue</blue-prop>
</diffuse>
<transparency-prop>transparency</transparency-prop>
<texture-prop>texture</texture-prop>
</animation>