Bug 1018237 - An option to link to webmaker.org and immediately start the login process

- <http://localhost:7777/signup?triggerUserLogin=new-account>
- <http://localhost:7777/signup?triggerUserLogin=existing-account>
- <https://webmaker.mofostaging.net/signup?triggerUserLogin=new-account>
- <https://webmaker.mofostaging.net/signup?triggerUserLogin=existing-account>
- <https://webmaker.org/signup?triggerUserLogin=new-account>
- <https://webmaker.org/signup?triggerUserLogin=existing-account>