Docker Image Update Policy

[tcaiazzi]

Add an option in the settings to manage the update of the Docker Images.

Actual behavior:
Every time a device is ran, Kathará checks if there are updates for the device image on the DockerHub. If there are, Kathará asks to the user (prompting on the terminal where Kathará is executed) if he wants to update the image.

Expected behavior:
The Kathará settings have an option to:

• Always update the images without prompting the request.
• Never update the images without prompting the request.
• Ask to the user the permission for doing the upgrade prompting the request (default).