Made addBean add the bean to the container. Casted getItem result to BeanItem[BT] and getItemOption result to Option[BeanItem[BT]] to make BeanItem available to the user of BeanItemContainer.
Merge pull request #29 from pallarij/beanitemcontainer

BeanItemContainer: addBean, getItem, getItemOption
Merge pull request #28 from hezamu/3.0

ShortcutAction support
Version 3.0.0.
Updated information about Scaladin 3
Fixes #44 - NPE in VaadinSession.setErrorHandler