Split the functionality of ConnectionWriterImpl into layers.

...s/net/sf/briar/transport/ConnectionReaderFactoryImpl.java

...s/net/sf/briar/transport/ConnectionWriterFactoryImpl.java

components/net/sf/briar/transport/ConnectionWriterImpl.java

.../net/sf/briar/transport/NullOutgoingReliabilityLayer.java

...s/net/sf/briar/transport/OutgoingAuthenticationLayer.java

...t/sf/briar/transport/OutgoingAuthenticationLayerImpl.java

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

test/net/sf/briar/transport/ConnectionReaderImplTest.java

test/net/sf/briar/transport/ConnectionWriterImplTest.java

test/net/sf/briar/transport/FrameReadWriteTest.java