Refactor test organization

[coilysiren]

• most tests should be in the folder for their app, eg.

callisto_core/
    delivery/
        tests/
    notification/
        tests/

• except for the webdriver / selenium / "functional" tests, which should stay in the callisto_core/tests/ folder, and that folder should be renamed to callisto_core/webdriver_tests/
• the callisto_core/wizard_builder/tests/test_frontend.py content should be moved to callisto_core/webdriver_tests/
• the tests in callisto_core/tests/callistocore/ likely all belong in callisto_core/delivery/tests/ (although some may be more relevant in callisto_core/reporting/tests/)