[airplay] - ensure to announce airtunes before airplay via zeroconf (makes it more likely that ios7 clients detect us correctly at the first shot)
[zeroconf] - add method to reannounce already published services
[airplay] - reannounce airplay service every 10 secs (fixes ios7 clients not detecting us when their wlan was asleep or they saw the airplay announcement before the airtunes annoncement)
Merge pull request #4414 from Memphiz/ios7airplayfix

[airplay] - fix regression introduced by ios7 clients