Option naxLevel added to UserNavigationTree. Closes #127
Invalid URI entry is now handled using an exception and exception
handler (InvalidURIExceptionHandler) in keeping with Shiro exception
handling.

I18NValue added but not yet tested
Invalid URI entry is now handled using an exception and exception
handler (InvalidURIExceptionHandler) in keeping with Shiro exception
handling.

I18NValue added but not yet tested
I18NKeys renamed I18NKey to be consistent with other enums
Renamed all enum <...>keys classes to <...>key
Tidied up I18N keys and values for consistency.  Introduced Notifier to
simplify use of Vaadin notifications with I18N.  Replaced a couple of
JMockit tests with Mockito
Rename TestLabelKeys to TestLabelKey
ErrorView displays stack trace.  Closes #164
Test results for previous commit