Instead we're going to move back to standard exceptions.
Using a custom Result class has created far far more problems
- The Stacktraces aren't always right
- Sometimes one forgets to check the Result error
- All other exception throwing code needing to be converted to Results
- Non idiomatic Dart code
I think it's better to just go back to exceptions. They have their
problems, but overall, I think it's a better approach.
Also added a full end-to-end test which uses the NoteEditor and types
some text + saves the note. This has taken more than an hour, but is
going to be very useful to improve GitJournal's reliability.
Fixes#604
