ERDs in YARD docs

[MSP-9821](https://jira.tor.rapid7.com/secure/RapidBoard.jspa?rapidView=84&view=detail&selectedIssue=MSP-9821)

Use yard-metasploit-erd to include ERDs in the YARD documentation for metasploit_data_models.  To support proper ERDs and fix warnings about RailsERD not being able to find inverse associations, I ported the addition from `inverse_of:` to all the associations from GREAT #1.