Original implementation to allow users to subscribe to labels

1. Allow subscribing (the current user) to a label

- Refactor the `Subscription` coffeescript class
  - The main change is that it accepts a container, and conducts all
    DOM queries within its scope. We need this because the labels
    page has multiple instances of `Subscription` on the same page.

2. Creating an issue or MR with labels notifies users subscribed to those labels

- Label `has_many` subscribers through subscriptions.

3. Adding a label to an issue or MR notifies users subscribed to those labels

- This only applies to subscribers of the label that has just been
  added, not all labels for the issue.

1 files changed, 4 insertions, 0 deletions

diff --git a/config/routes.rb b/config/routes.rb
index 780ad757c5b..2ae282f48a6 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -675,6 +675,10 @@ Rails.application.routes.draw do
           collection do
             post :generate
           end
+
+          member do
+            post :toggle_subscription
+          end
         end
 
         resources :issues, constraints: { id: /\d+/ }, except: [:destroy] do