Gem skeleton

[MSP-9815](https://jira6.osdc.lax.rapid7.com/secure/RapidBoard.jspa?rapidView=11&view=detail&selectedIssue=MSP-9815)

Skeleton with all the [Metasploit-specific changes](https://github.com/rapid7/pro/wiki/Creating-a-gem-in-the-Metasploit-namespace)