Feature: Slack integration (#783)

- Integrations architecture
- Slack integration

spec/models/integrations/hook_spec.rb

@@ -0,0 +1,12 @@
+require 'rails_helper'
+
+RSpec.describe Integrations::Hook, type: :model do
+  context 'with validations' do
+    it { is_expected.to validate_presence_of(:app_id) }
+    it { is_expected.to validate_presence_of(:account_id) }
+  end
+
+  describe 'associations' do
+    it { is_expected.to belong_to(:account) }
+  end
+end