rename project name (tutorial -> essentials)
rename package name
Merge branch 'master' into chapter9

Conflicts:
	src/main/java/org/zkoss/essentials/chapter4/SidebarChapter4Controller.java
	src/main/java/org/zkoss/essentials/chapter5/mvc/ProfileViewController.java
	src/main/java/org/zkoss/essentials/chapter5/mvvm/ProfileViewModel.java
	src/main/java/org/zkoss/essentials/chapter6/mvc/TodoListController.java
	src/main/java/org/zkoss/essentials/chapter6/mvvm/TodoListViewModel.java
	src/main/java/org/zkoss/essentials/chapter8/AuthenticationInit.java
	src/main/java/org/zkoss/essentials/chapter8/LoginController.java
	src/main/java/org/zkoss/essentials/chapter8/LogoutController.java