Little code clean-up;
'Zoom all' operation has been implemented with new display API;
Panning has been implemented.
Unused code (after new display implementation) has been removed;
More general QPainter is used for drawing;
Convinitint constuctors (initializer lists) have been added to geometry;
Thumbnail symbols have been implemented (only 3 - poin, polyline, polygon);
Code clean-up;