Understand async code in js to test it

[tobydragon]

done when:
The async code is written correctly and there are tests checking that the Comm package works correctly

[tobydragon]

3 hours so far: js has a complex concept of Promises that required a lot of reading an thought to apply. Made the getFromServer work with Promises, and bonus recognize server errors now in the client. Still need to:

• write tests for getFromServer and PostToServer
• Fix postToServer