Now test is updated for new Message.py
Added a heartbeat (optional)
Changes 'data_type' to 'name'
More generic publisher and subscriber
Renamed old publisher and subscriber
Now genreral heartbeat for Publisher

Better handling of adding and removing addresses
Longer default timeout
Better handling of adding and removing addresses
Easy access to all nameserver addresses
'address' are prepended to message subject
Cosmetic
Cleaner interface to adding and removing addresses
Preparing for publishing of removal of addresses
Now importing time
Printing ZMQ exception
Improved address listener
Better port 0 checking

Now possible to easy subclass Publish
Better default topic 'pytroll:/'
Added address as optional argument top Subscribe
Now,  service="" means all services and service=None means no services