[OSX] fix a bug where it is not possible to submit app to Mac App Store

We have to do the code sign twice to submit app

1. code sign to app with
  "3rd Party Mac Developer Application: XXX"

2. code sign to pkg with
  "3rd Party Mac Developer Installer: XXX"

lib/motion/project/template/osx/builder.rb

@@ -31,7 +31,12 @@ module Motion; module Project
       archive = config.archive
       if !File.exist?(archive) or File.mtime(app_bundle) > File.mtime(archive)
         App.info 'Create', archive
-        sh "/usr/bin/productbuild --quiet --component \"#{app_bundle}\" /Applications \"#{archive}\""
+        codesign = begin
+          if config.distribution_mode
+            "--sign \"" + config.codesign_certificate.sub(/Application/, "Installer") + "\""
+          end
+        end || ""
+        sh "/usr/bin/productbuild --quiet --component \"#{app_bundle}\" /Applications \"#{archive}\" #{codesign}"
       end
     end