Separated the subject line from the message body.

api/net/sf/briar/api/protocol/Message.java

api/net/sf/briar/api/protocol/MessageEncoder.java

components/net/sf/briar/protocol/MessageEncoderImpl.java

components/net/sf/briar/protocol/MessageImpl.java

components/net/sf/briar/protocol/MessageReader.java

test/net/sf/briar/ProtocolIntegrationTest.java

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

test/net/sf/briar/db/H2DatabaseTest.java

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

test/net/sf/briar/protocol/ProtocolReadWriteTest.java

test/net/sf/briar/protocol/writers/ConstantsTest.java

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