VideoIframe from YouTubeVideo (simplified) + VimeoVideo
using named keys and format string method + renaming VideoIframe to VideoIFrame
IFrame + ScribdDocument
tabulation adjustment
generic IFrame(src, with, height), refactored YouTubeVideo, VimeoVideo, ScribdDocument
Merge pull request #3200 from 3kwa/master

add base IFrame class, and YouTubeVideo siblings, VimeoVideo and ScribdDocument