Switch reindexer to use slf4j.

The reindexer as as accessed by:
```
bin/omero admin reindex
```
should log using logback to `stderr`. This command works with a local server and using a fresh database the `--full` option should generate about 40 lines of logging. An alternative console log config file can be used:
```
JAVA_OPTS="-Dlogback.configurationFile=etc/logback-cli.xml" bin/omero admin reindex --full
```
should produce a little more output.