Assign the session[:user_id] in development

Previously, despite signing in a dummy user, this wasn't happening.

app/controllers/application_controller.rb

@@ -16,9 +16,11 @@ def current_user
       user = nil
 
       # In the development environment, your current_user will be the
-      # first User in the database. Easy enough ;-)
+      # first User in the database or a dummy one created below.
       if !Rails.env.production?
         user = User.first_or_create(email: "alvar@hanso.dk", name: "Alvar Hanso")
+        session[:user_id] = user.id
+        flash[:notice] = "Signed in!"
       else
         user = User.find(session[:user_id]) if session[:user_id].present?
       end