workflow_QC: plot width should not affect PCA

[KarinSchork]

The plot_width in the workflow_QC function currently affects all plot types.
There should be two different widths/heights, one for the plots that depend on the number of samples (e.g. boxplots, valid value plots) and one for the PCA.

[KarinSchork]

and also separate settings for MA-Plots?