tutorial: Connecting to an External database (GrantaMI)

## Description
Thoughts, plans and issues related to the 'Connecting to a database' section of the tutorial workshop: a 2-4 hour tutorial for the BDSS.

This will make use of the GrantaMI plugin: https://github.com/force-h2020/force-bdss-plugin-granta-example

## Related Issues
One of the topics in #4, design of tutorial workshop.