Update to mejs 2.11.0 and template jquery compatibility fix

Hello,

Made some updates to the contao-medialement. I've tested it with jQuery but not with mootools since I don't have a setup using mootools right now.
* Updated to media element 2.11.0
* Fixed loading issue when jQuery present on page (https://github.com/terminal42/contao-mediaelement/issues/6)

Feel free to check, edit and take the bits you want. (Note only issue I've had is it couldn't run videos on the latest OS Safari but I couldn't figure out whether it was the host, mejs or the contao extension)