Bug 49117 [Plan Item] Workbench needs hooks for new welcome support
M6 We need to provide an extension point and some interfaces to allow for a primary feature to declare a welcome page. This extension point will be tied the new IProduct being defined by the Core team and needs to have 3 states 1) Fill whole screen 2) Collapsed on the right when the user selects something and starts working 3) Disables when it is no longer of any use
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/ide/IDEWorkbenchAdvisor.java
private static final String WORKBENCH_PREFERENCE_CATEGORY_ID = "org.eclipse.ui.preferencePages.Workbench"; 
	/**
	 * The dialog setting key to access the known installed features
	 * since the last time the workbench was run.
	 */
	private static final String INSTALLED_FEATURES = "installedFeatures"; 
	
	private static IDEWorkbenchAdvisor workbenchAdvisor = null;
	/**
	 * Special object for configuring the workbench.
	 */
	private IWorkbenchConfigurer configurer;	
	/**
	 * Event loop exception handler for the advisor.
	 */
	private IDEExceptionHandler exceptionHandler = null;
	
	/**
	 * Tracks whether we were autobuilding.
	 */
	private boolean autoBuild;
	/**
	 * Contains the workspace location if the -showlocation command line
	 * argument is specified, or <code>null</code> if not specified.
	 */
	private String workspaceLocation = null;
	/**
	 * Set of versioned feature ids from previous session; <code>null</code>
	 * if uninitialized. Element type: <code>String</code>
	 */