```drop_rows_with_outliers()``` currently not working

[Gerhardsa0]

Describe the bug

When calling the drop_rows_with_outliers-function on Table-object, the data in the table gets lost.

This failed on a large dataset(the titanic dataset).

To Reproduce

Steps to reproduce the behavior:

1. create a Table
2. call the Table.drop_rows_with_outliers()-function
3. see that all the values of the table are missing

Expected behavior

Only the outliers of the table should be removed

[lars-reimann]

This happens if any of the numerical columns has a missing value. In that case scipy.stats.zscore returns NaN for any value in that column and NaN < 3 is False. Because of this, all rows are dropped.