Unify command-line importer help

Fix https://trac.openmicroscopy.org.uk/ome/ticket/12010

- Use OMERO username and OMERO password
- Capitalize ID across the board

To test this PR, compare the output of

```
$ bin/omero import -h
$ bin/omero import --javahelp
```

And make sure the argument descriptions are consistent with each other. Once these upstream changes are validated, I will open a corresponding documentation PR.