Add version checking that shows on the admin dashboard

lib/discourse_updates.rb

@@ -0,0 +1,41 @@
+module DiscourseUpdates
+
+  class << self
+
+    def check_version
+      DiscourseVersionCheck.new(
+        latest_version: latest_version || Discourse::VERSION::STRING,
+        installed_version: Discourse::VERSION::STRING,
+        critical_updates: critical_update_available?
+        # TODO: more info, like links and release messages
+      )
+    end
+
+    def latest_version=(arg)
+      $redis.set latest_version_key, arg
+    end
+
+    def latest_version
+      $redis.get latest_version_key
+    end
+
+    def critical_update_available=(arg)
+      $redis.set critical_updates_available_key, arg
+    end
+
+    def critical_update_available?
+      ($redis.get(critical_updates_available_key) || false) == 'true'
+    end
+
+
+    private
+
+      def latest_version_key
+        'discourse_latest_version'
+      end
+
+      def critical_updates_available_key
+        'critical_updates_available'
+      end
+  end
+end