Basic asdi support

### Rationale
ADSI support was missing, it was needed, so now it's not missing!

This PR starts the basics of the ADSI support for Meterpreter. It lives in the `ext_server_extapi` module. The current code supports the ability to run generic queries. For full details see the [MSF side](https://github.com/rapid7/metasploit-framework/pull/2736) of this PR.