FIX: under some conditions draft would say it was saving when not

This is a major change to draft internals. Previously there were quite a
few cases where the draft system would say "draft saved", when in fact
we just skipped saving.

This commit ensures the draft system deals with draft ownership handover in
a predictable way.

For example:

- Window 1 editing draft
- Window 2 editing same draft at the same time

Previously we would allow window 1 and 2 to just fight on the same draft
each window overwriting the same draft over an over.

This commit introduces an ownership concept where either window 1 or 2 win
and user is prompted on the loser window to reload screen to correct the issue

This also corrects edge cases where a user could have multiple browser windows
open and posts in 1 window, later to post in the second window. Previously
drafts would break in the second window, this corrects it.

app/controllers/draft_controller.rb

@@ -11,7 +11,41 @@ class DraftController < ApplicationController
   end
 
   def update
-    Draft.set(current_user, params[:draft_key], params[:sequence].to_i, params[:data])
+    sequence =
+      begin
+        Draft.set(
+          current_user,
+          params[:draft_key],
+          params[:sequence].to_i,
+          params[:data],
+          params[:owner]
+        )
+      rescue Draft::OutOfSequence
+
+        begin
+          if !Draft.exists?(user_id: current_user.id, draft_key: params[:draft_key])
+            Draft.set(
+              current_user,
+              params[:draft_key],
+              DraftSequence.current(current_user, params[:draft_key]),
+              params[:data],
+              params[:owner]
+            )
+          else
+            raise Draft::OutOfSequence
+          end
+
+        rescue Draft::OutOfSequence
+          render_json_error I18n.t('draft.sequence_conflict_error.title'),
+            status: 409,
+            extras: {
+              description: I18n.t('draft.sequence_conflict_error.description')
+            }
+          return
+        end
+      end
+
+    json = success_json.merge(draft_sequence: sequence)
 
     if data = JSON::parse(params[:data])
       # this is a bit of a kludge we need to remove (all the parsing) too many special cases here
@@ -20,16 +54,21 @@ class DraftController < ApplicationController
         post = Post.find_by(id: data["postId"])
         if post && post.raw != data["originalText"]
           conflict_user = BasicUserSerializer.new(post.last_editor, root: false)
-          return render json: success_json.merge(conflict_user: conflict_user)
+          render json: json.merge(conflict_user: conflict_user)
+          return
         end
       end
     end
 
-    render json: success_json
+    render json: json
   end
 
   def destroy
-    Draft.clear(current_user, params[:draft_key], params[:sequence].to_i)
+    begin
+      Draft.clear(current_user, params[:draft_key], params[:sequence].to_i)
+    rescue Draft::OutOfSequence
+      # nothing really we can do here, if try clearing a draft that is not ours, just skip it.
+    end
     render json: success_json
   end