(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)



By default, I'd expect it would be mounted under a "hopefully-unique" prefix.  I suppose with this being configurable via the web routing service that a user could create a situation where this app would be mounted at the same endpoint as another app.  In that situation, the `not-found` route could prevent both apps' routes from being fully evaluated.  This would seem like a very bad idea for a user to create such a conflict, though.  If there's no other rationale that comes to mind for not doing this, then, I'm good with it.