This commit cleans up code in the Secured class and provides a test class for Secured.

Classes:
- Account: Add attribute isTestAccount to deny login of test users on frontend
- Secured: Code clean up and improvements, add JavaDoc
- FakeApplicationTest: Add JavaDoc to attributes, add methods getConfiguration(), getAccountByEmail(), getAdminAccount(), getGroupByTitle(), getTestGroup(), getGroupAccount(), establishGroupMembership(), removeGroupMembership(), loginAdminAccount(), getContext()
- MockNotifiable: Implement method getNotification()
- ApplicationTest: Remove sample class as it is not needed
- IntegrationTest: Remove sample class as it is not needed
- SecurityTest: Add class to test Secured class
- WebSocketTest: Affected by renaming of FakeApplicationTest::loginTestAccount() to FakeApplicationTest::loginAccount()

Other:
- messages: Add i18n for expired session error message