away-notify and away rate limiting added

Referenced:

atheme/charybdis@c5bbc6037579a3c4b72b2a9910138950c628a8d8 : Add
away-notify client capability.
atheme/charybdis@d42e6915cf1002f5d5df2677d8f2a9225a0857c0 : Pace aways.
atheme/charybdis@725403fd7f78716db000b0847f81ac346d4e98b6 : Don't end
the flood grace period with the first AWAY.
atheme/charybdis@dc0fd46236fe65a18ce082707c3fade81a689f68 : Ensure AWAY
pacing only affects local clients.