Add humanize_name option to CSVBuilder#column to control humanization of column name.
Add humanize_name option to CSVBuilder too and pass it to its columns.

This allows a much DRYer code if you have many column namess you don't
want to be humanized. As a bonus, any other transitive option like this
one can be added easily in the future.
Add other test for humanize_name on CSVBuilder.
Merge pull request #3145

Conflicts:
	lib/active_admin/csv_builder.rb