Performance test

I added a variant of the violinplot.R function (-> add_violinplot()), that returns the dashboard instead of the component. So there is no need to call i2dash::add_component. The increase of performance when using the wrapper is enormous! There is no loadingtime anymore. (it was a test, therefore the check if the provided page exists is not in the code.) I think, it could be worth to think, whether we adapt the structure for other functions instead of using add_component() from i2dah.