Feature/rest calls

- Apologies for the large PR, fixing the tests took some refactoring
- To make the demux executors non-blocking, I added some become/unbecome logic 
- Moved the request work to the executors and they will only pass the request up to parent if they are idle. Not sure if this is ideal
- Return response codes from the api endpoints

Doesn't this handle the missing message case now? I don't know about the timeout though? I guess you'd have to wrap it all in a  `try ... catch` to pick up the timeout case?