Update Virtual Appliance documentation for Docker Toolbox

Kitematic has been replaced by [Docker Toolbox](https://www.docker.com/products/docker-toolbox), documentation and screenshots at https://planemo.readthedocs.io/en/latest/appliance.html#launching-the-appliance-docker need to be updated accordingly.

Start with the “Launching the Appliance (Docker)” section of the Virtual Appliance documentation at https://planemo.readthedocs.io/en/latest/appliance.html#launching-the-appliance-docker. Compare its Kitematic instructions and screenshots with the current Docker Toolbox workflow, then update the documentation and screenshots so the section no longer refers to Kitematic.

Written by the indexing model from the issue text.