only run player::update on the server

also add function in world to determine if we are a server.
will have to add that instead of doing if (m_server...etc hardcoding
improve velocity calculations
fix movement jittering, don't send player movement after kick for malicious

i was accidentally sending a player movement command if it was malicious,
after we kicked them. we probalby deleted their player, too and were
doing a null deref. accidentally moved the code around and broke it, seems.

the big problem that was present was the movement jittering, which after
a long while of tracing it from the inner parts of the world/player, into
server, then realizing client was sending it, then seeing that qt was
sending a release event when i wasn't releasing...only to realize
it was because of key auto repeat. so, ignore those key repeat events.

hard to believe it was something so simple. but then again, 90% of the time
it is a simple fix that's hard to track down. i was surprised that the
jitteriness was so intermitten though. i guess it's probably because i
have a high repeat interval