[FEATURE] Processing plot refactoring

[ghtmtt]

This is a first PR that refactors completely the Processing interface.

Code idea:

• single DataPlotlyProcessingPlot class with all the parameters and plot creation
• using plotly.express and pandas
• one class for each plot type inheriting from main one (does everything automatically)

From user point of view:

• (for now) scatter and bar plots available in Processing
• usable in the modeler

should be also easier to add other plot types with their specific parameters