Currently, realm-js errors do not give much of useful information.
Failed-to-login should be: no such server, server not responding, no such database, wrong credentials, wrong db instance, protocol version not supported, whatever.
The 10 most common errors must be recognized and relayed to UI.

relay error codes and messages for:

• [x] network errors
• [x] auth errors
• [ ] database errors
• [ ] local errors

Check two cases of each in RealmTasks and Realm Browser.
Add unit tests for those cases.