Split client/server tests for model management.
ModelManagementTestCase now contains setup/teardown, frame imports and model creation.
ApiTestCase (derived class) contains API tests.
SteamTestCase (derived class) contains GUI tests.

To run just one of the two, use:

python testdir_model_management/test_model_management.py -ccj localhost.json ApiTestCase

or

python testdir_model_management/test_model_management.py -ccj localhost.js SteamTestCase