Changes:
- added missing unit tests
- introduced PopupsContextTestWrapper, removed all unit-tests logic
from Hooks/Context classes
- removed getModule() from Popups.hooks.php, it's hooks responsibility
to keep single context instance
- removed class_exists calls, use ExtensionRegistry instead
- pass ExtensionRegistry as a dependency so it's easy to mock
- reach 100% code coverage
- introduce PoupsContext::isBetaOn() as it was used in many places
Change-Id: Id014efe72edf24628539c76968e53eb3e06709f4
