AODAAC challenge captcha

Solving #1214 and #1216 by adding a challenge (captcha) to AODAAC downloads.

This work also unifies AODAAC and Gogoduck controllers into AsyncDownloadController which will handle both and route to either service depending on the `aggregatorService` passed to it. I think now the test coverage is also better.
This can just be `if (!jobParameters) {...` we're in Groovyland now.

![magic](https://cloud.githubusercontent.com/assets/2774917/3680535/95b6a908-12af-11e4-9f94-c95eeffe3398.gif)