Bug 64419 Tomcat example does not need "web app root" attribute
The Tomcat/JSP launching example currently requires the user specify a "web app root" on the main tab. However, all we need is the project (in order to compute a classpath for extra java files and source lookup path). We used to require the attribute for source lookup.
org.eclipse.jdt.ui.examples.javafamily/src/org/eclipse/jsp/launching/TomcatTab.java
String expansion;
		try {
			expansion = VariablesPlugin.getDefault().getStringVariableManager().performStringSubstitution(workingDirPath);
		} catch (CoreException e) {
			setErrorMessage(e.getMessage());
			return false;
		}
		if (workingDirPath.length() > 0) {
			File dir = new File(expansion);
			if (!dir.exists()) {
				setErrorMessage(LaunchingMessages.getString("TomcatTab.5")); 
				return false;
			}
			if (!dir.isDirectory()) {
				setErrorMessage(LaunchingMessages.getString("TomcatTab.6")); 
				return false;
			}
		}	
		
		String webappDirPath = fWebAppDir.getText().trim();
		if (webappDirPath.length() > 0) {
			IResource resource = ResourcesPlugin.getWorkspace().getRoot().findMember(new Path(webappDirPath));
			if (resource == null) {
				setErrorMessage(LaunchingMessages.getString("TomcatTab.30")); 
				return false;
			}
			if (!(resource instanceof IContainer)) {
				setErrorMessage(LaunchingMessages.getString("TomcatTab.31")); 
				return false;