Improve SVQC command flood control

Changes to the same logic used by chat flood control which is more
progressive.  The previous command flood control was only triggered if a
client managed to send more than 8 commands within 1 second, and then
it reset immediately.

Prints an informative message when flood control blocks a command.
Previously this was silent.

Special cases the client's initial connect commands, as these would
otherwise trigger the new flood logic with the current default settings.

Exempts chat commands from command flood control, as these have their
own flood control.

Simplifies the code for max perf.