Bug 520392 - Hard coded error message when entering an empty string in
direct editing

* Add method getDirectEditingInvalidNotificationTitle in tool behavior
provider to override the default popup title
* Default implementation of tool behavior provider returns the standard
string
* Had to move the text definition from the UI to the core plugin
* Added example implementation in tutorial

Change-Id: I129321898825fa1a4e569039a984698c23dab0b0