function loadPackage(themePackage) {
        var fileName = themePackage.path + "/" + themePackage.metadata.theme.file;
        return loadFile(fileName, themePackage.metadata);
    }
Loads a theme from an extension package.

@param {Object} themePackage is a package from the extension manager for the theme to be loaded.
@return {$.Promise} promise object resolved with the theme to be loaded from the pacakge