Added web hooks functionality

This commit includes:

 * Projects can have zero or more WebHooks.
 * The PostReceive job will ask a project to execute any web hooks defined for that project.
 * WebHook has a URL, we post Github-compatible JSON to that URL.
 * Failure to execute a WebHook will be silently ignored.

db/migrate/20111214091851_create_web_hooks.rb

@@ -0,0 +1,9 @@
+class CreateWebHooks < ActiveRecord::Migration
+  def change
+    create_table :web_hooks do |t|
+      t.string :url
+      t.integer :project_id
+      t.timestamps
+    end
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20111207211728) do
+ActiveRecord::Schema.define(:version => 20111214091851) do
 
   create_table "issues", :force => true do |t|
     t.string   "title"
@@ -132,4 +132,18 @@ ActiveRecord::Schema.define(:version => 20111207211728) do
     t.integer  "project_access", :default => 0, :null => false
   end
 
+  create_table "web_hook_urls", :force => true do |t|
+    t.string   "url"
+    t.integer  "project_id"
+    t.datetime "created_at"
+    t.datetime "updated_at"
+  end
+
+  create_table "web_hooks", :force => true do |t|
+    t.string   "url"
+    t.integer  "project_id"
+    t.datetime "created_at"
+    t.datetime "updated_at"
+  end
+
 end