Add BB tag for YouTube videos to news and forum.

Usage example: [youtube]wK0w0x62PjA[/youtube]

The video frame is responsive, so that in case the width of the page is narrower than the default 560px of YouTube embed it will shrink to fit.
![screenshot from 2014-10-23 15 59 11](https://cloud.githubusercontent.com/assets/3932953/4754254/dc65968e-5abc-11e4-9044-882f64b604f9.png)

Live demo is available here: http://ot.forgee.se/index.php

If you see something you would like done differently let me know.