Add relative date filter option to select dates before given period

This is an extension of the current relative date filtering options from MDL-72662 (last/current/next) to include a Before option

e.g. "Select everything where the timestamp is [before] [3 days] ago"

Original report (actual use case)

Summary: Not logged in for x period

Extra function for showing users in de report who are not logged in for x period or x date.