main project is set which defines a <code>ProjectConfigurationProvider</code> and lists the available
 configurations in alphabetical order. If <code>hasCustomizer()</code>, a final entry <b>Customize…</b> is added
 which if selected just invokes <code>customize()</code>.
</p>
<p>
 Main-project-specific toolbar buttons are given an extra combo-box-like dropdown menu when a main project is
 set, it has a <code>ProjectConfigurationProvider</code> with multiple configurations available,
 and <code>configurat