Additional unittests for researcher side

This merge request includes following changes:

• Completing unit tests for Job class
• Moving unit tests in test_check_data_quality.py into test_job.py
• Extending methods in FakeResponses to make it compatible with Job class
• FakeModel for testing loading model as python module from path
• Completing unit tests for Monitor class
• Adding unit tests for Aggregator and FedAvg classes
• Adding unit tests for localJob
• Fixing bug in test_requests.py when running unit tests in parallel

Changes After review

• Replace properties with getters as getter() in Responses and FederatedDatasets
• Update Job and Experiment classes based on changes in Responses and FedereatedDatasets
• Update notebooks to use new getters of Responses class