API error handling

In the final video of this module, we're going to setup error handling for the Vuex ORM Axios Plugin.

Once we add authentication to our frontend app in the next module, most of the important errors will be dealt with the auth plugin, since most of the API errors we encounter will be auth errors, for example invalid password, or token.

However, there are some others kinds of errors that we want to deal with at the store level.