Renamed user-defined tags "user-defined type identifiers".

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

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

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

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

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

api/net/sf/briar/api/serial/Reader.java

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

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

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

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

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

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

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

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

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

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

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

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

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

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