Merge branch 'note-query-information' into 'master'

Note query information

The 'editable' field is required to be able to distinguish system-created notes from user comments. The 'upvote' and 'downvote' fields are so that endpoints don't need to duplicate GitLab's logic for what an up or downvote is.

See merge request !677

doc/api/notes.md

@@ -31,7 +31,10 @@ Parameters:
       "state": "active",
       "created_at": "2013-09-30T13:46:01Z"
     },
-    "created_at": "2013-10-02T09:22:45Z"
+    "created_at": "2013-10-02T09:22:45Z",
+    "system": true,
+    "upvote": false,
+    "downvote": false
   },
   {
     "id": 305,
@@ -45,7 +48,10 @@ Parameters:
       "state": "active",
       "created_at": "2013-09-30T13:46:01Z"
     },
-    "created_at": "2013-10-02T09:56:03Z"
+    "created_at": "2013-10-02T09:56:03Z",
+    "system": false,
+    "upvote": false,
+    "downvote": false
   }
 ]
 ```

lib/api/entities.rb

@@ -190,6 +190,9 @@ module API
       expose :attachment_identifier, as: :attachment
       expose :author, using: Entities::UserBasic
       expose :created_at
+      expose :system
+      expose :upvote?, as: :upvote
+      expose :downvote?, as: :downvote
     end
 
     class MRNote < Grape::Entity