Backend switch over to hermes

This merges the current develop into master. Includes functionality for hermes backend that can be used by running: 

```export TERMINUS_HOST='dashboard.getpantheon.com'```
...Though I think for now I'm fine punting if we just change the `if TERMINUS_HOST = <hardcoded_domain>` to just `if TERMINUS_HOST_IS_DEFINED then <use TERMINUS_HOST>` because this is still all alpha and requires that TERMINUS_HOST be passed in. Which I think allows us to push forward while addressing the concern of hardcoding the URL.