Add test for integration arguments in bin/omero import
Add integration test for --annotation_link argument of CLI import
Isolate get_object() and get_annotation_link() in test_import.py
Add integration tests for screen/dataset arguments
Fix integration test for screen argument of CLI import

For some reasons, the fake SPW creates a screen at import so we must retrieve
all screens linked to the plate and make sure the linked screen is among them
Add docstrings to the CLI import test methods