0030619: Draw Harness, ViewerTest - add continuous rendering option to vrepaint command

0030619: Draw Harness, ViewerTest - add continuous rendering option to vrepaint command

Aspect_Window::InvalidateContent() - added new virtual method for invalidating window content using platform-specific API.

TKDraw, tkLoop() on Window platform has been changed so that to prevent
continuous input window events blocking terminal input
(e.g. in case if processing events is not fast enough or
if another continuously sends new events).

TKViewerTest, on X11 platform has been fixed a message processing
so that to avoid messages being not processed.
Added aggregation of Exposer and ConfigureNotify events.
Fixed aggregation MotionNotify events.