Redirect all controllers to login if required

We want to skip the filter for sessions controller so that we can login
and we want to skip the filter for static pages because those should be
visible to visitors.

app/controllers/application_controller.rb

@@ -22,6 +22,7 @@ class ApplicationController < ActionController::Base
   before_filter :preload_json
   before_filter :check_xhr
   before_filter :set_locale
+  before_filter :redirect_to_login_if_required
 
   rescue_from Exception do |exception|
     unless [ ActiveRecord::RecordNotFound, ActionController::RoutingError,
@@ -280,6 +281,10 @@ class ApplicationController < ActionController::Base
       raise Discourse::NotLoggedIn.new unless current_user.present?
     end
 
+    def redirect_to_login_if_required
+      redirect_to :login if SiteSetting.login_required? && !current_user
+    end
+
     def render_not_found_page(status=404)
       f = Topic.where(deleted_at: nil, archetype: "regular")
       @latest = f.order('views desc').take(10)