Add JSDoc to marionette.helpers

Used a bunch of descriptions from https://github.com/Puppets/marionette-docs/blob/master/api/helpers/helpers.md
I think if we write it as `Marionette.getOption` it will be smart enough to make this connection. Per the docs, this is for when you do like:

```js
/**
  * @memberof Marionette
  */
var myFn = function() {};

Marionette.myFn = myFn;