Database methods for expiry updates and expiry acks.

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

briar-api/src/net/sf/briar/api/protocol/ProtocolWriter.java

briar-core/src/net/sf/briar/db/Database.java

briar-core/src/net/sf/briar/db/DatabaseComponentImpl.java

briar-core/src/net/sf/briar/db/JdbcDatabase.java

briar-core/src/net/sf/briar/protocol/ProtocolWriterImpl.java

...re/src/net/sf/briar/protocol/duplex/DuplexConnection.java

.../sf/briar/protocol/simplex/IncomingSimplexConnection.java

.../sf/briar/protocol/simplex/OutgoingSimplexConnection.java