Manifest Tool v2.1.1rc3

• Remove support for Python 3.5.
• In v1 schema, allow creating manifests without the priority field.
• Changes to the manifest-dev-tool:
  • Fix usage of https://api.us-east-1.mbedcloud.com as default Pelion Device Management API URL.
• Changes to the manifest-dev-tool update command:
  • Add --use-short-url option. Using this option decreases manifest size.
    Note: The device must be configured to use CoAP.
  • Add --gw-preset option, which enables presetting an access key in a .pelion-dev-presets.yaml file in the home directory.
  • Print campaign summary on tool exit.
  • Upload firmware images smaller than 100MB with the /v3/firmware-images API.
• Improve the tool help and the README.md.