capability: handle NULL passed to capability_get().

Referenced https://github.com/atheme/charybdis/commit/d7e4ed772f3b98e7c95bac8bb3775df9adbcee11 : capability: handle NULL passed to capability_get(). by mogri
Merge: atheme/charybdis/ac0707aa61d9c20e9b09062294701567c9f41595

m_capab: fix a possible remote crash triggered by the CAPAB parsing code
Away rate limiting added

Referenced:

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.
Add Charybdis' /REMOVE

atheme/charybdis/925c50efea6d2e1c14bfb456918dcc5bef24091f : Add implementation of /REMOVE, based on ircd-seven implementation.
Editor did not save file when instructed to, names refactored to make sense
Updated RESV FNC logic

atheme/charybdis/330692a1f28d6b722350550c4901fcbc38a87b08 : Add option to immediately apply nick RESVs by FNC'ing.
atheme/charybdis/07d3283f382c9bb201c7b72dfbe058e22b3c407e : RESV FNC: Sign off/on monitor, and don't try to FNC users that already have a UID nick.
Ensure all signals keep working after a SIGINT restart.

atheme/charybdis/f8904200144052c16f9bc58ed3bf7887bdcd7b02 : Ensure all signals keep working after a SIGINT restart.
Add missing server notice for failed SVSLOGIN commands

atheme/charybdis/ec57fe6779dcd827578088bfeb1610f7ebde4e0e : Complain to opers if a server that isn't a service tries to SU/RSFNC/NICKDELAY/SVSLOGIN.
Add server notice for kills

atheme/charybdis/45ed8835846fc4749f4eb058ddc409184a661ee4 : rsfnc/svslogin: Add server notices for kills.
Missed a brace
Updated todo
Add away-notify support

atheme/charybdis/c5bbc6037579a3c4b72b2a9910138950c628a8d8 : Add away-notify client capability.