Renamed frame cipher -> segment cipher, frame key -> segment key.

api/net/sf/briar/api/crypto/CryptoComponent.java

components/net/sf/briar/crypto/CryptoComponentImpl.java

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

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

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

.../sf/briar/transport/IncomingSegmentedEncryptionLayer.java

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

.../sf/briar/transport/OutgoingSegmentedEncryptionLayer.java

test/net/sf/briar/crypto/KeyDerivationTest.java

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

...t/sf/briar/transport/IncomingEncryptionLayerImplTest.java

...briar/transport/IncomingSegmentedEncryptionLayerTest.java

...t/sf/briar/transport/OutgoingEncryptionLayerImplTest.java

...briar/transport/OutgoingSegmentedEncryptionLayerTest.java