Removes bundler dev dep.

Bundler is already a dep of jeweller, plus the version restriction made
it so I couldn't bundle because I have 1.1.5
Adds gateway_test spec helper.

I think we should put this into core to make it easier to test plugins.
Adds success_status and success_message.
Merge pull request #1 from bhenderson/add_success_status_and_message

Add success status and message