Enrollment activity by track

@clintonb @shnayder @mulby @WatsonEmily @mhoeber @catong @srpearce 
This enhancmeent is expected to be released later this month
"the number of students who have chosen an honor certificate, who have chosen a verified certificate, or who are enrolled..." (It's clunky, but it's parallel.) :-| Or maybe "the number of honor code certificate, verified certificate, or professional education students"? Again, :-|.