```
"http://localhost:8888"
"http://localhost:8888/"
"http://127.0.0.1:8888"
"http://127.0.0.1:8888/"
"8888"
8888
```
Ideally these should converge to the same thing. Since many hash
tables are keyed off `url-or-port`, forgetting to
normalize `url-or-port` with `ein:url` leads to missed cache hits and
general malaise. So we try to do that.
Address a FIXME: apply callbacks to `ein:notebook-list-login-and-open`.
Removed py3.5 from travis build matrix to reduce developer strain.
