Improved ToolItem implementation

Known issues: 
* It uses internal API - it should rather use default lookup API if possible
* Missing default constructors (lookup via indexes,...)
* Sub-item menu support ref - https://github.com/jboss-reddeer/reddeer/issues/34
* Combine API with ToolBarMenu (it should be one implementation regardless ToolItem has menu or not)

Yeah, you're right. But also ReferenceComposite is used when there might be some ambiguous situation while searching for widget - however only one shell can be focused at once, so no ambiguity can happen.