use rwlock for multipeer.
fix #15
ServiceNames(). fixing #13
use RWMutex when possible.
use rwmutex
NrConns, NrUsers. fixing #13
tested concurrent get add del with dup conns in connmap.
AllUsernames() in srvCenter. fixing #13
AllUsernames(). fixing #13
fixing #13.
fix #13.
changed the push notification content to make it small.
forgot a comma.