Overflow: hidden was cutting of info in the play view. Without it in the new home page, though,
infinite banners would expand the size of the page. Tried figuring out a way to not make the new
page require hiding overflow but found no obvious solution. Pages with infinite banners will
just need to be set to overflow: hidden individually.
This patch makes iframe borders render identically in all supported browsers (i.e. no border).
Although Chrome does not displays borders around iframes by default, Firefox and Edge (IE) had visible iframe borders prior to this patch. This is because, as [previously mentioned](https://github.com/codecombat/codecombat/pull/3122#discussion_r42338590), the DOM property was mistyped as `frameborder` when it should be `frameBorder`.
As this is presentational issue, it feels more appropriate to fix it using CSS. Therefore, I've removed the buggy JS code and added a generic CSS solution to reset iframes' border styling.
