ThemeableBrowser OverrideUserAgent/AppendUserAgent Not working

#1

The ThemeableBrowser plugin is not having the support for OverrideUserAgent / AppendUserAgent which is available in the InAppBrowser plugin. Due to this, I’m unable to vary the user agent string when the pages are opened in Themeable Browser. Please provide support for that. Refer the open pull requests https://github.com/initialxy/cordova-plugin-themeablebrowser/pull/72 for IOS & https://github.com/initialxy/cordova-plugin-themeablebrowser/pull/71 for Android.