ENH: Added AbstractModel::IsModified(); Tested IsModified() when closing window/quitting application.

ENH: Improved VectorImageModel::Settings to keep track of modified and applied flag (replacing old dirty flag); Cought MainWindow::closeEvent() and displated confirm save/discard/cancel dialog.

ENH: Managed load vs. import image-models from file(s) in DatasetModel; Parsed loaded DatasetDescriptor in DatasetModel to reload imported images.

ENH: Improved DatasetDescriptor::GetImageModel() method (reading of input image information from XML DOM).

ENH: Moved creation of empty XML DOM into DatasetDescriptor::BuildDocument(); Improved ::virtual_BuildModel() to build in-memory XML DOM or to read it from file (if a non-NULL and valid ::BuildContext(filename) argument has been provided); Improved ::Read() method; Added qDebug() messages in ::Read() and ::Write() methods; Moved code into ::BuildDocument() method.

ENH: Moved DatasetDescriptor XML tag names from #define to static constants (reason: need usage in inline methods).

ENH: Moved DatasetDescriptor XML tag names into #define constants; Changed DatasetDescriptor::CreateContainerNode< TContainer >() to ::CreateContainerNode< TInputIterator >() to comply with STL algorithm pattern; Added image ID to DatasetDescriptor::InsertImageModel().