* Add drag'n'drop support for ensemble summary vectors and ensembles into histogram plots
* Make sure histogram plot is shown and all update signals are connected when loading a project.
* Support ensemble parameter drag'n'drop from data sources into histogram plots.
* Show ensemble parameters in data sources tree.
* Add copy/paste of histogram curves
* Re-use all existing parameters in a plot when dragging a new ensemble into it
The std::unique_ptr<RiuPlotWidget> would delete the widget when
RimHistogramPlot object was recreated. This would lead to a
double-delete since the RiuPlotWidget was already deleted by Qt
through the parent-child relationship.
Fixed by using QPointer, and leaving the cleanup to Qt.
JJ
Kristian Bendiksen