Added support for using the @ionic/cli package (https://www.npmjs.com/package/@ionic/cli), as ionic is deprecated ( https://www.npmjs.com/package/ionic).
If selecting latest for ionic version or a major version greater or equal than 6 (6, 6.10.1), then will install the new ionic package.
ionic 5 is still installed if required, but it is recommended to upgrade.
Using the latest LTS node.js version is recommended (https://nodejs.org/).
See release notes, for updating to ionic CLI 6: https://github.com/ionic-team/ionic-cli/blob/develop/packages/%40ionic/cli/CHANGELOG.md#600-2020-01-25)
Turned off using legacy Xcode build system by default, as cordova-ios 5.0.0 supports it (https://cordova.apache.org/announcements/2019/02/09/cordova-ios-release-5.0.0.html).