Double-Click zoom trigger no longer works

Setting the zoom trigger to Double-Click no longer works. This is due to the localization changes, which now stores the localization key rather than the translation as the menu setting value. So the check for trigger name in MathMenu.js should be for DoubleClick rather than Double-Click.

That is easily fixed, but if a page author has set the menuSettings.zoom to the old value of "Double-Click" this will no longer work. So we should either have MathMenu.js look for both, or have MathJax convert Double-Click to DoubleClick during configuration.