Make fetch async

[Per Wiklander]

I sometimes get this message in the console when using PotMap:

Warning: DiodeWrapper is accessing isMounted inside its render() function.
render() should be a pure function of props and state. It should never
access something that requires stale data from the previous render,
such as refs. Move this logic to componentDidMount and componentDidUpdate instead.

It looks like the problem is that the mapHandler in AsyncActionRetriable wants to set the value of the Pot to Pending right away. If this happens while rendering, React gets cranky.

[Otto Chrons]

This is due to PotMap calling fetcher synchronously, which updates the model and causes a chain of calls that result in a call to isMounted in the ReactConnector. I'll update PotMap to always call fetcher in an async fashion to avoid this (and other potential related problems).

[Otto Chrons]

Fixed in ece23b6