Use `DimensionsPickerAction` from the core instead of local copy

[alxvth]

Use a setup like

    auto dimensionsGroupAction = new GroupAction(this, "Dimensions", true);

    dimensionsGroupAction->addAction(&inputDataset->getFullDataset<Points>()->getDimensionsPickerAction());
    dimensionsGroupAction->setText(QString("Input dimensions (%1)").arg(inputDataset->getFullDataset<Points>()->text()));
    dimensionsGroupAction->setShowLabels(false);

    outputDataset->addAction(*dimensionsGroupAction);

as in the t-sne plugin to reduce code duplication with the core.