Added lazyness to OWScatterPlot by specifying regions of interest.
lazytable.py:
- Region of interest support in LazyTable and LazyRowInstance
owlazyfile.py:
- Region of interest support in OWLazyFile.
owscatterplot.py:
- Region of interest and LazyTable support in OWScatterPlotQt.
owscatterplotgraph.py:
- Removed OWScatterPlotGraphQt to prevent confusion.
- Added propagate_region_of_interest(), hooked to mouseMoved.