Simplified auth plugin

Simplified version of #1763 

Introducing auth service.
- Stores persona.
- Handles building/destroying Permissions and Auth plugins (moved from AppController)
-Privacy directive uses it.
- Fix #1759 (The replies permissions were not filled, only the reading permissions
because privacy directive used to fill the rest. But a change made it not to touch the permissions of an annotation which has the permissions already set.)

This might read more clearly as:

```coffee
if newValue is oldValue
  if isFirstRun
    $scope.login()
else
  reset()
```

But it's up to you.