An alert is now shown when the user switches from an account that is
connected to the active tab to an account that is not connected. The
alert prompts the user to dismiss the alert or connect the account
they're switching to.
The "loading" state is handled by disabling the buttons, and the error
state is handled by displaying a generic error message and disabling
the connect button.
The new reducer for this alert has been created with `createSlice` from
the Redux Toolkit. This utility is recommended by the Redux team, and
represents a new style of writing reducers that I hope we will use more
in the future (or at least something similar). `createSlice` constructs
a reducer, actions, and action creators automatically. The reducer is
constructed using their `createReducer` helper, which uses Immer to
allow directly mutating the state in the reducer but exposing these
changes as immutable.
Mark Stacey