Add the ability to set number of excluded rows between groups

[huskerdrew]

Create the functionality to hide and exclude rows between groups to function as a buffer. IE... choose a group size of 4 groups but I want 2 rows between groups to be hidden and excluded. This also gives us the "less rows stratified" as a special case. Example: group size of 1 row but hide and exclude 7 rows as a buffer. This would then only include every 8th row.