Class which contributes a checkbox to an intro page which allows welcome to show
on startup. If the checkbox is checked the home page of intro will be shown the next
time the Eclipse application starts up. This class may be subclassed to override
the text for the checkbox label.
Implements the IIntroContentProvider to create the checkbox ui, and the
org.eclipse.ui.intro.config.IIntroAction interface for handling checkbox click events.
Dispose of the ContentProvider. This will only be called when the Intro
view is closed. In other words, the content provider will not be disposed
of until the last possible minute. This gives the implementor the chance
to cache content and avoid regenerating content on every page switch.