Create Graph of Database Schema as SVG

Discussion: https://twitter.com/zippy1981/status/1124282065116127233

Continuation of the work in #17

Best options look like: 

* [A free closed source Apex project](https://www.apexsql.com/sql-tools-model.aspx)
* [This python based tool that uses graphviz tool](https://github.com/rm-hull/sql_graphviz)
