* ( bug 21373 ) improved mwEmbed localization support

* ( bug 21373 ) improved mwEmbed localization support
** switched to uselang param to specificity language
** fixed outputpage and mv_embed url language param handling accordingly

* added msg version check to script-loader (checks the latest version of any msg text and updates the unique request key)
* added associated configuration flag: $wgScriptModifiedMsgCheck

* general msg updates and centralization of mwe-cancel and mwe-ok