Store group as an instance variable
Add helper methods for 11479
Add non-reproducing method (See #11479)

This method attempts to reproduce the described error
from 11479. An ERR is returned during the chmod, however,
preventing the test from completing:

```
Cannot change permissions on ome.model.meta.ExperimenterGroup:Id_1162 to rw---- due to locks:
  {*=1, ome.model.annotations.ProjectAnnotationLink=1}
```
Reworked test to clearly show the issue (root!)

For some reason, the root user and not a group admin
can perform these changes. Currently looking into why
this could be.
Perform check in omero.group=-1 (Fix #11479)
Merge pull request #2369 from joshmoore/11479-private-tags

11479 Private Tags Bug