implement Fit Classifier/Regressor/Transformer/Clusterer algorithms combining individual algorithms

[Andreas Rabe]

Discussed in with the team.

E.g. for Fit Classifier, put all individual classifier into a new algorithm, where a classifier can be selected from a combobox:

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To achieve this, we need a new custom processing parameter widget that includes the combobox, the code editor widget and description text widget.

[Andreas Rabe]

We need that for the “Regression-based unmixing” algorithms.

[Andreas Rabe]

implemented custom processing parameter for selecting estimators, e.g. Regressors

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[Andreas Rabe]

Already implemented Classification/Regression Workflow algorithms.

Todo: Transformation and Clustering Workflow algorithms, see #1134 and #1135

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