adjust the parameters of the flippant.flip function for better control o...

[armish]

...ver the back element.

Changed the parameter content to the HTML element--that is the back of the card/modal--with the name back.

The older way was flawed in the sense that, when the back element was created, it was being appended to the body hence reducing the control over the flippand.

To better understand this, imagine a scenario where the developer wants to destroy the flipped card (i.e. the back element) when the user requests a new view (the Backbone-way). With the older way, it was incredibly hard to destroy the back element.

If the developer specifies the back element by himself (as this commit allows), s/he can destroy the container of the card/modals and will simply get rid of the overflowing back element whenever a new view is created.

Just a suggestion ;)