Feature: Slack integration (#783)

- Integrations architecture
- Slack integration

app/models/integrations/app.rb

@@ -0,0 +1,51 @@
+class Integrations::App
+  attr_accessor :params
+
+  def initialize(params)
+    @params = params
+  end
+
+  def id
+    params[:id]
+  end
+
+  def name
+    params[:name]
+  end
+
+  def description
+    params[:description]
+  end
+
+  def logo
+    params[:logo]
+  end
+
+  def fields
+    params[:fields]
+  end
+
+  def button
+    params[:button]
+  end
+
+  def enabled?(account)
+    account.hooks.where(app_id: id).exists?
+  end
+
+  class << self
+    def apps
+      Hashie::Mash.new(APPS_CONFIG)
+    end
+
+    def all
+      apps.values.each_with_object([]) do |app, result|
+        result << new(app)
+      end
+    end
+
+    def find(params)
+      all.detect { |app| app.id == params[:id] }
+    end
+  end
+end