Add column counts as default, independently from table showing it

[shajoezhu]

rtables result data frames do not report column N’s. These numbers are available from the TableTree object but may not be straightforward to retrieve. This is NOT considered as a critical feature to have, because whenever a frequency is calculated, n and % are often (if not always) reported in the rtables result data frame, and column N could then be calculated (i.e. if n and % are correct, N should be correct). However, it would be nice to explore ways to get this column N into the result data frame of rtables