Add conversations API (#8832)

* Add conversations API

* Add web UI for conversations

* Add test for conversations API

* Add tests for ConversationAccount

* Improve web UI

* Rename ConversationAccount to AccountConversation

* Remove conversations on block and mute

* Change last_status_id to be a denormalization of status_ids

* Add optimistic locking

spec/controllers/api/v1/conversations_controller_spec.rb

@@ -0,0 +1,37 @@
+require 'rails_helper'
+
+RSpec.describe Api::V1::ConversationsController, type: :controller do
+  render_views
+
+  let!(:user) { Fabricate(:user, account: Fabricate(:account, username: 'alice')) }
+  let(:token) { Fabricate(:accessible_access_token, resource_owner_id: user.id, scopes: scopes) }
+  let(:other) { Fabricate(:user, account: Fabricate(:account, username: 'bob')) }
+
+  before do
+    allow(controller).to receive(:doorkeeper_token) { token }
+  end
+
+  describe 'GET #index' do
+    let(:scopes) { 'read:statuses' }
+
+    before do
+      PostStatusService.new.call(other.account, 'Hey @alice', nil, visibility: 'direct')
+    end
+
+    it 'returns http success' do
+      get :index
+      expect(response).to have_http_status(200)
+    end
+
+    it 'returns pagination headers' do
+      get :index, params: { limit: 1 }
+      expect(response.headers['Link'].links.size).to eq(2)
+    end
+
+    it 'returns conversations' do
+      get :index
+      json = body_as_json
+      expect(json.size).to eq 1
+    end
+  end
+end