(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)



Yes, because the current packaging for PE and FOSS puts the "certificate-authority" section in a file called 'ca.conf', which doesn't currently contain anything at all except for the cert-status auth info.  removing that would leave that file empty, which just seemed like it would cause too much turmoil for packaging.