Key derivation function based on NIST SP 800-108.

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

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

test/net/sf/briar/ProtocolIntegrationTest.java

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

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

.../net/sf/briar/transport/ConnectionRecogniserImplTest.java

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

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

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