Database backup filenames contained a colon character, which is disallowed
on Windows; use period instead

See #1676

* Add email-based password reset

Fixes #734

* rename SETPASS to RESETPASS

* review fixes

* abuse mitigations

* SENDPASS and RESETPASS should both touch the client login throttle
* Produce a logline and a sno on SENDPASS (since it actually sends an email)

* don't re-retrieve the settings value

* add email confirmation for NS SET EMAIL

* smtp: if require-tls is disabled, don't validate server cert

* review fixes

* remove cooldown for NS SET EMAIL

If you accidentally set the wrong address, the cooldown would prevent you
from fixing your mistake. Since we touch the registration throttle anyway,
this shouldn't present more of an abuse concern than registration itself.

Track channel join times, use them to optionally enforce history access
restrictions

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

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

* limit the total number of registrations per account
* when an account is unregistered, unregister all its channels

Automatically create the datastore on `oragono run` if it doesn't exist.
See also #302.

1. Implement persistent channel keys (#208)
2. Persist changes to registered channel modes
3. Backend changes for persisting operator status (partial #198)