New feature and API base url change

• Add an option to publish JUnit XML files to Zephyr Scale Cloud;
• Adjust the plugin to use the new Zephyr Scale API base url: https://api.zephyrscale.smartbear.com/v2

Note that previous versions of the Jenkins plugin will not work anymore from 15/06/2021, when the current API base URL becomes deprecated in favor of the URL change described above.