Fixes #1740

Transition most "is an operator" checks to require a specific operator
capability

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

Explicit quit and ping timeout behave the same way,
but reattach after abandoning/losing the previous session
(without the break being detected server-side) is more aggressive
about replaying missed messages, at the cost of potential duplication.

* Fix #679 (borked reply to `JOIN #chan,\r\n`)
* Replace invalid error parameters with *'s in various places
* Fix PART with no message sending an empty trailing parameter to the channel
* Fix some error responses not getting labeled

Some clients seem to automatically poll for channel state

1. Remove leaveClientIdle (unused)
2. s/leaveClientActive/leaveClientIdle/
3. make ISON a leaveClientIdle command (some clients send it periodically
   if a /msg window is left open)

1. Handle PROXY lines with IPv6 addresses starting with ::
(similar to WEBIRC in issue #211)

2. Strip v6 mapping from v4 addresses when handling proxied IPs.