Changes to the background state were being detected in the `update`
event handler in `ui/index.js` that receives state updates from the
background. However this doesn't catch every update; some state
changes are received by the UI in-between these `update` events.
The background `getState` function is callable directly from the UI,
and many action creators call it via `forceUpdateMetamaskState` to
update the `metamask` state immediately without waiting for the next
`update` event. These state updates skip this change detection in
`ui/index.js`.
For example, if a 3Box state restoration resulted in a `currentLocale`
change, and then a `forceUpdateMetamaskState` call completed before the
next `update `event was received, then `updateCurrentLocale` wouldn't
be called, and the `locale` store would not be updated correctly with
the localized messages for the new locale.
We now check for background state changes in the `updateMetamaskState`
action creator. All `metamask` state updates go through this function,
so we aren't missing any changes anymore.