Add a delayed auto-voice to chanserv

[DasBrain]

(Labels: Chanserv Enhancement)

Add a channel setting to voice all joining users after a delay.

Rationale:
Delaying the ability to speak in the channel for unregistered people is a good mitigation strategy against the current spam attack.
This can be archived by setting the channel mode +DM (delay join, reg-only moderated), and auto-voicing anyone who enters with a delay.

If a fixed delay is used, a chanflag can be used.
If the delay should be configurable on a per channel basis, then more changes are needed.