implement hotbar item dropping, fix some state synchronization issues

make more clear some assumptions, like the server will tell a client
the new stacksize, if that is 0 it is implied that the client will delete
the item on their end.

fix some member vars not getting copied properly in the copy ctor of Item

don't handle key press/release if we're unconnected.

verified a few more things on the server, instead of blindly accepting them
(only a couple had this issue).

hotbar dropping is yet untested, so probably doesn't work. need to commit
because i have some other client networking fixes + improvements i want to
see, including packet limiting, bunch of other security things..
set slightly saner packetsize and buffer size on server

set to like 4MB, which is quite huge considering the things were sending
don't seem to exceed 1MB..or get even close.
properly ignore quickview autorepeat keyboard events