Support for streamed remote service invocation responses

[eliaslindholm]

Add support to stream response from server to client:

interface WizerImportService {
    @AstrixStreamed
    Observable<TransactionRecord> getTransactions();
}

// Service implementation
class WizerServer implements WizerImportService {
    @Override
    public Observable<TransactionRecord> getTransactions() {
        return Observable.create(new OnSubscribe<TransactionRecord>() {
            @Override
            public void call(Subscriber<? super TransactionRecord> t1) {
                try {
                    for (TransactionRecord record : streamRecordsFromDisk()) {
                        t1.onNext(record);
                    }
                    t1.onCompleted();
                } catch (Exception e) {
                    t1.onError(e);
                }
            }
        });
    }
}

// Example consumption pattern
class WizerClient {
    WizerImportService wizerImport;

    public void runWizerImpor() {
        wizerImport.getTransactions().doOnNext(processTransaction());
    }

    private Action1<? super TransactionRecord> processTransaction() {
        return new Action1<TransactionRecord>() {
            @Override
            public void call(TransactionRecord t1) {
                // process t1
            }
        };
    }
}