Import structured logging gem ougai and replace current use of puts/warn with
logging calls.  Gives us level, timestamp, and formatting for exceptions and/or
hash of arbitrary context data.  Can do JSON logging if we ever need that, but
set to human-readable (with colour if isatty) for now.

* btc_spop:
  Get new Bitcoin address from Redis set

This set is populated by a cron job to have only known-good available addresses
in it.

So it won't be taken as next by naive code.

Instead, adhoc bot will show the options for actions to take

Not on our inbound-facing JID.  This is why we shouldn't be mucking in the SGX's
Redis at all...

Turns out every user will start with no attempts, and the code wasn't
handling that case. Oops.

Not typing indicators, etc.

Notify only once per day (using expiring redis key).
Can notify MUC or user, always sends directed presence first so it will join MUC
if not joined.
Ignore all messages direct to the component, mostly to throw out live messages
from MUC if we join that to notify.

Just gives them the information and we're done. Support has to manually process
these payments anyway.

To show mailing address, eTransfer address, Bitcoin addresses, and allow
generating a new Bitcoin address.

An invalid customer id is an error from braintree, so handle the error and
return an empty list of payment methods.

Also rename buy credit to top up

And use that in registration instead of implementing it inline

So say feature-not-implemented if we haven't got it with some other handler.

* conditionally-show-commands:
  Only show buy credit option if customer has a plan and a credit card
  Show commands conditionally (plus add voicemail record command)

Refactor to a factory that allows commands to be shown conditionally, so that
the voicemail record command can only be shown if the customer has a forwarding
target set up.