Improve auditability of sensitive operator actions

strip local_ from oper capab names, also consolidate unban into ban

Fixes #1380

Enhancements to NS SUSPEND, including stored metadata and the ability
to list suspensions

CLIENTS LIST shows information about clients attached to a nick.
CLIENTS LOGOUT allows individual (or all) sessions to be logged out.

SESSIONS is now an alias for CLIENTS LIST.

Fixes #1072.

These commands search the registered nicknames/channels for ones
matching the provided regex, or return the entire list.

Only operators with chanreg (for ChanServ) or accreg (for NickServ)
capabilities can use LIST.

Or try to, anyway

In the previous commit, the client would receive a failure message but would
actually remain logged in after an authzid/authcid mismatch. This was a
correctness rather than a security issue, but now it's fixed so that the client
never logs in in the first place.