Change the api to return full TODO list after adding todo

[Larocceau]

Addresses #615 in a more conclusive manner:

• Test failed because it lacked loading the initial data; because the added todo was mapped into a RemoteData type, data disappeared quietly when that RemoteData object was not in the Finished state yet.
• Solution: Make the API return the full todo list, so you can fully replace the todo list after an update