Notify user on error
Notify user on error

I'm assuming that `addError` displays an error.

I'm also logging the error on the console - for theoretical debugging in case the notification is dismissed - but maybe it's unnecessary.
I renamed `event` to `error` in the `onupgradeneeded` handler
PKRoma/atom,atom/atom,brettle/atom,PKRoma/atom,Mokolea/atom,PKRoma/atom,brettle/atom,atom/atom,atom/atom,Mokolea/atom,Mokolea/atom,brettle/atom