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.

spec/requests/projects_tree_perfomance_spec.rb

@@ -9,7 +9,6 @@ describe "Projects" do
       before do
         @project = Factory :project
         @project.add_access(@user, :read)
-
       end
 
       it "should be fast" do