broker/Topic: String Topics replaced by Topic class
broker/Topic#parseTopic: access set to private
broker/SubscriptionsStoreTest: topic tests moved to own class
broker/TopicTest: containsExactly used
broker/TopicTest: TopicAssert class added
broker/TopicTest$TopicAssert#containsToken: method added
broker/TopicTest$TopicAssert#matches: method added