Add eclipse.appName System Property for setting the Display's AppName

The eclipse.appName sytem property allows users to specify on the
command line the appName to be used for a specific Eclipse instance. The
appName Display property is used by window managers and
desktop environments for identification and grouping. This is helpful to
distinguish Eclipse instances (e.g., JDT vs CDT) as per default these
all are using the same identifier.

eclipse-packaging/packages#253

bundles/org.eclipse.ui.workbench/eclipseui/org/eclipse/ui/internal/Workbench.java

@@ -747,9 +747,8 @@ static Object getApplication(@SuppressWarnings("unused") String[] args) {
 	 * @return the display
 	 */
 	public static Display createDisplay() {
-		// setup the application name used by SWT to lookup resources on some
-		// platforms
-		String applicationName = WorkbenchPlugin.getDefault().getAppName();
+		// setup the application name used by SWT to lookup resources on some platforms
+		String applicationName = System.getProperty("eclipse.appName", WorkbenchPlugin.getDefault().getAppName()); //$NON-NLS-1$
 		if (applicationName != null) {
 			Display.setAppName(applicationName);
 		}