Error handling for layers

[ericboucher]

Handle errors when fetching data.

In particular, have the ability to parse time mismatch "Time dimension value '2020-02-10' not valid for this layer".

And server errors (eg. server offline)

[ericboucher]

Linked to #7

[bencpeters]

Redux state now has an errors array in MapState (and an error string for table state and server dates).

We should probably just add a snackbar to display any errors.

This could potentially be implemented using a Redux middleware too.

[Ry-DS]

@laveesh and I are looking into implementing one of the two react notification APIs

1. https://teodosii.github.io/react-notifications-component/
2. https://toasted-notes.netlify.app/

Creating the notification will be pretty easy - just a function call.

We could do this two ways:

1. Make a redux middleware and check every action that passes through.
   • If we see an action that we know counts as an error (e.g action.type === 'mapState/loadLayerData/rejected') we can read the payload and create the notification there.
2. Edit the reducers themselves to create a notification.
   • By editing every reducer that counts as storing an error (e.g in serverStateSlice) we can just create the notification there.

Which do you think is better for the long run?

[Ry-DS]

Update: After some discussion with @laveesh, we've decided to use Material UI's built in Snackbar.

We also will be taking approach 1 to make things more stable in the long run (and as @bencpeters suggested).

Look out for a PR!