Added methods: UrlNavigator::historyIndex(), UrlNavigator::historySize(). Added signal UrlNavigator::historyChanged(). Changed return meaning in UrlNavigator::goForward() and UrlNavigator::goBack().
Disable Back/Forward buttons when they can't be used.
Add history menu. Add UrlNavigator::setHistoryIndex() method.
* Move MainWindow member variables initialization to constructor list.  * Add "Go Up" and "Refresh" actions to File menu.  * Minor MainWindow source code formatting.
Update bookmark open handling
Improved bookmark loading and add / delete operations.