improve divider perfs
reintroduce divider
tweak featured game socket messages
don't forget to unsubscribe round actor on stop
improve ping and featured game propagation performances
so I checked and `val mutable` is faster than `var immutable`.
use a socket user register to accelerate communications
fix decline challenge doesn't warn the opponent
name all socket actors for logging
use mutable map for socket actor members
use a mutable map to store ActorMap actors
remove dead code, count rounds less often
fix socket unsubscribe
rename socket hub events
crawlers need no game divisions
Merge branch 'master' of https://github.com/ornicar/lila into HorizPGN