1.42 Fix #5 and #6.

*Fix HTML5 progress bar not resizing. Thanks to [YePpHa](https://github.com/YePpHa/) for solving this bug in YoutubeCenter. [[Screenshot](https://i.imgur.com/FcLISVq.png)]
* Fix the player getting right aligned in some cases. [[Screenshot]](https://greasyfork.org/forum/uploads/FileUpload/95/4d455197513c65d1aa243a0d800133.jpg)
* Prevent the script from running twice on the same page.