News reading app improvements

- SAXPArser no longer used; custom parser implemented
- News article list provides only article titles (no longer feed title)
- pim.NewsStoring.countNewArticleInGroup() added
- News group list shows number of unread articles
- app.news.NewsGroupWrapper class added for data associated with news groups
- NumberUtil class for Russian language added
- Delete key in groups list marks all articles as read; backspace does the action reversed to tab
- Minor language improvements
New popup approach with no multiple copies of the same popup protection

- core.Popup interface introduced
- All classes inside of popup package support new Popup interface
- PopupRegistry class moved to PopupManager
- PopupEventLoopStopCondition gets onNewCopyLaunch() method to notify current instance should be disabled
- PopupManager gets onNewCopyLaunch() method to disable all popups of the particular class
- Environment openPopup() and openPopupByApp() methods added
- No more Environment.onOpenEvent method
- Luwrain.openFile(), openFiles() (instead of open()) and openPopup() methods is added
- Luwrain.popup() method now takes only a reference to Popup interface
- All necessary changes to reflect new features