CLI import help changes (rebased onto develop) (rebased onto dev_5_0)


This is the same as gh-2772 but rebased onto dev_5_0.

----


This is the same as gh-2766 but rebased onto develop.

----

Another set of changes for the CLI import suggested by @manics.
To test this PR, check the ouput of

- ``bin/omero --java-help`
- ``bin/omero --advanced-help``