- HistogramLUTItem avoids using lookup table if possible
- GradientEditorItem has a method to ask whether the gradient is trivial (can be applied without the use of a lookup table)
- ROI, LinearRegionItem, InfiniteLine no longer redraw for every mouse movement
Moved GraphicsScene to its own directory, added exportDialog
Removed old export options from PlotItem / ViewBox (will re-enable once they are working again)