Add JSDoc to marionette.helpers

Used a bunch of descriptions from https://github.com/Puppets/marionette-docs/blob/master/api/helpers/helpers.md
oh wait, nvm. I was confused. I like them at the top actually. I think of them as an extension of the description.

Because of that, I think it's weird to go

Description, data, description.

I prefer description, description, data.