(SERVER-113) admin http endpoint

This commit adds a new TK service and HTTP endpoint for puppet
admin functionality.  For now, it just has a placeholder
"/hello" route, but the scaffolding is in place for wiring
in the real functionality, including:
    
* Support for client whitelist configuration
* Versioned routes (just /v1 for now)



Yeah.  I probablye won't get a chance to update this PR though, so you may just need to fix this in the follow-up PR, or close this and add a commit on top of my branch.