Simplification attempt of svc-auth.js

@settinghead Please review.

I've stripped out everything from `svc-auth`, so I've probably broken your modal logic for other stuff in the header. I think it makes sense though to keep that stuff in a separate service, and keep `svc-auth.js` pristine, and only related to the auth flow and user state, etc.

I also unknowingly started with a slightly earlier version of your `common-header.js` (form the *dist* directory) so it uses the templates in `common-header.html` instead of the templateCache. There is very little change in the header templates though, so you will be able to port that over really quickly.