grouping_key_for method when params[:group] == "week" always returned "#{date.cweek}/#{date.year}" but that not always is true.
When a date belongs to the first_week/last_week of the year we have exceptions for example "31/12/2018". His cweek is equal to "1", old code returned "1/2018" value but correct result would be "1/2019".
FIxed issue in last commit: supports controller were not correctly
filling the holes without data.
Fixed duplication in supports and successful supports controller using a
concer.
Successfull supports controller will fill the holes without data in the
same way that supports controller does.
