[platform-ui-dev] Preliminray code for "pluggable looks" is in head

[Stefan Xenos <Stefan_Xenos@xxxxxxxxxx>]

Okay... I've committed some preliminary
code for pluggable look-and-feel. PartTabFolder is now using the new object
model, so it should be a 1-line change to make use of a plugin-provided
renderer.

https://bugs.eclipse.org/bugs/show_bug.cgi?id=53673

The package org.eclipse.ui.internal.skins
contains the classes that will be promoted to API once everything is ready.
The package org.eclipse.ui.internal.skins.newlook contains classes specific
to the Eclipse 3.0 "new look".