* 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
Simplifies color handling by replacing transparency settings with opacity for curve and fill colors.
This change provides a more intuitive user experience and ensures consistent behavior across the application.
- Renames "ColorTransparency" to "ColorOpacity" for RimCurveSetAppearance.
- Introduces "CurveColorOpacity" for RimPlotCurveAppearance.
- Updates blending calculations to correctly use opacity.
- Adjusts UI slider attributes for opacity settings, including minimum, maximum and decimals.