Add dependency on gatekeeper and verify visibility permissions

@kentquirk @jh-bate 

These are the changes to pool-whisperer to get it to verify permissions.

Gatekeeper (https://github.com/tidepool-org/gatekeeper) is a new repo I created to house the server and the client.  I went ahead and just checked things into master and released v0.0.1 as it works with this.  I wanted to get it published to npm sooner to make this PR more complete, so I didn't do a PR there.  Feel free to comment on stuff/make changes over there as well, however.

I'd like to push this as part of the current set of things to devel.  So, if you could look at it sooner rather than later, it'd facilitate that.