Fix for #261 - add in-app header

@settinghead @stevesherrie please review
In theory you can load gadget via a lazy-loading service, and structure controller & template in such a way that if gadget api is never called, it is never loaded (https://github.com/Rise-Vision/common-header/blob/master/src/js/svc-gapi.js#L48)

However this is pretty complicated to implement, so I'm fine with leaving it the way it is now and come back later if gadget client is proven to be a requirement across many apps. Thanks.