Refactor score detail tooltip into metrics helper

I had a wrong understanding of when to use helpers. I thought helpers
only carry code which is used by both, view and controller. This code,
however, rather belongs into the controller.

View helper carry code to construct markup code. Hence, I have started
to refactor the score detail tooltip construction into the helper.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>