Move reduceDataFrame from QFeatures to MsCoreUtils

[lgatto]

I am using QFeatures::reduceDataFrame() in PSMatch, which now depends on the former just for that (low-level) function. What about moving this file from QFeatures to MsCoreUtils?

@sgibb @jorainer

[jorainer]

Looks good to me. Question: that does only work for DataFrame, right? Any plans to have that implemented for data.frame too? And also, most NumericList etc have the parameter compressed = TRUE, how does your function work with that? I had the impression that compressed lists are slower.