[WIP] PublisherLatched

[randaz81]

• added the new class yarp::os::PublisherLatched
• added test to PublisherTest

From http://wiki.ros.org/roscpp/Overview/Publishers%20and%20Subscribers#Publisher_Options : "When a connection is latched, the last message published is saved and automatically sent to any future subscribers that connect. This is useful for slow-changing to static data like a map."

[update-docs[bot]]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would update the release notes by adding a file in doc/release/<target_branch>, based on your changes.

[drdanz]

As discussed with @randaz81, this PR requires several changes, I'm marking this as draft...

[randaz81]

withdrawn because yarp ros component will be become unmaintened/deprecated