introduce "flat ip" representations

This didn't work correctly for IPv6 or custom nets.
/UNDLINE IP can temporarily be used to reset the throttle.

fix #1439, give all atheme group founders +q

Validate imported databases for confusable nicks

{default,traditional}.yaml: refer to IPs/CIDR instead of addrs

Whenever CIDR is mentioned in the config, it's in combination with IP so
talking about addressese in these points gives wrong impression that a
domain name would be valid as those are often thought as addresses.

fix some bugs

change FAIL codes from NOT_PRIVED to PRIVS_NEEDED

fix #1403

Handle the case where atheme had a successor, but didn't correctly
elect them as founder (?)

fix #1428

fix #1431

fix #1426

I think that 'moderator vs admin' is a pretty common set of priv levels,
whereas 'oper vs admin' is a little confusing, esp. to less irc-savvy
people.

/SAJOIN and /SAMODE are really common for joining channels to check out
what's going on and for e.g. opping someone when nobody in the channel
is opered, so it makes sense for mods to have those. I feel similarly
about vhosts, they're usually something that's delegated to less-prived
opers.

Changed the whois line from 'a server admin' to 'the server admin' to
make it a bit more clear that this is one single user, rather than a set
of privs to be shared. And it's a tiny thing, but removed the 'less
privileged' term from alice's oper block because it felt a bit dodgy.

Tor listeners should never see an STS cap.

Add an undocumented 'hide-sts' key for listeners that hides the STS cap.
This can be used if the listener is secured at layer 3 or 4 (VPNs,
E2E mixnets). It will be necessary to add the relevant IPs to `secure-nets`.

See #1426

fix #1421

Allow custom limit definitions that encompass multiple subnets

fix #1345

validate amode recipients during data import

enhancements to database import

atheme2json enhancements

Convert the flat list of channels for always-on clients
to a map from channel names to channel-user modes.

Store the channel-user modes of always-on clients along with their
channel memberships, restore them on server startup. This will coexist
alongside /CS AMODE, which autoapplies modes to clients on join regardless
of their always-on status.

fix #1417

Allow `JOIN 0` with a confirmation code

fix TAGMSG being relayed to clients without message-tags

more memory-efficient implementation of line reading

fix #1409

fix #1396

add network name to RPL_WELCOME