Video Streams page could block usage of unavailable ports or show a list of those

Blake was having a problem were he was trying to add a new UDP stream (for his exploreHD camera), but it was failling. @joaoantoniocardoso came to the conclusion it was because there were endpoints already using that port (for the regular USB camera, that was not connected).

If we show a list with the unavailable ports, or issue a warning when the user tries to use an unavailable port, we can prevent those situations.

This is specially important for cases were people are using multiple cameras, which is more and more common.