Converted database events from an enum to classes to allow them to

api/net/sf/briar/api/db/DatabaseComponent.java

api/net/sf/briar/api/db/event/BatchReceivedEvent.java

api/net/sf/briar/api/db/event/ContactAddedEvent.java

api/net/sf/briar/api/db/event/ContactRemovedEvent.java

api/net/sf/briar/api/db/event/DatabaseEvent.java

api/net/sf/briar/api/db/event/DatabaseListener.java

api/net/sf/briar/api/db/event/MessagesAddedEvent.java

api/net/sf/briar/api/db/event/SubscriptionsUpdatedEvent.java

api/net/sf/briar/api/db/event/TransportsUpdatedEvent.java

components/net/sf/briar/db/Database.java

components/net/sf/briar/db/DatabaseComponentImpl.java

components/net/sf/briar/db/JdbcDatabase.java

...ents/net/sf/briar/transport/ConnectionRecogniserImpl.java

components/net/sf/briar/transport/stream/Flags.java

...nents/net/sf/briar/transport/stream/StreamConnection.java

test/net/sf/briar/db/DatabaseComponentTest.java

...f/briar/transport/batch/BatchConnectionReadWriteTest.java