Change login and login error actions to server actions.

The server authenticates a user so actions based on data from the server should call `handleServerAction`
Use correct Emitr API when emiting a change.

Pass in context to `addChangeListener` to allow Emitr to call listeners with correct function scope.
Pass in HeaderElement scope to `addChangeListener`.
HeaderConstants values need to be unique.
Add in simple styling for initial HeaderElement load.