Prevent all undefined player parameters being appended to YouTube embed query string, added `playsInline` option to enable inline playback on iOS, enable YouTube API to be loaded from `file://` URIs

I've made 3 changes to enable the use of this plugin in `UIWebViews` in iOS apps (e.g. via PhoneGap/Cordova) and have updated the documentation and minified version accordingly. Feel free to automatically merge the lot or cherry-pick the changes to `media.youtube.js` as you wish!