Add support for flippable content with dynamic height/width

[Download]

Currently, Flip fixes the width and height of the content by adding width and height styles forcing dimensions in pixels. In my fork I prepared a version of Flip that does not do this, allowing the width and height to be controlled from the stylesheet and be percentages so it shrinks/expands with the container it's in.

[timcv]

+1

[softdays]

+1 (I have to use Download's fork to flip content with dynamic height)

[JemarJones]

+1 This should definitely be merged, it just makes sense.