Cronjob to check pending BTC transactions

When they become confirmed, insert them into the transactions table.
We can never double-insert because of the PRIMARY KEY on transaction_id, so the
script is always safe to run even if something ends up in redis twice.
Endpoint that pushes all unknown transactions into Redis

The intent is to use `electrum notify <address> <app>/electrum_noify?address=&customer_id=`

The app asks electrum for all transactions on that address, and then checks
which ones we *don't* already have recorded in the transactions table.  These
are pushed into Redis to be picked up by a to-be-written job that will write
them to the transactions table after 3 confirmations.
Save bidirectional association for customer_id in redis
Hide loading spinner on error so the error state can show
In production, require customer_id be passed also.

As a security measure, so people can't modify the cards on arbitrary JIDs.
Add magic comment
Going to use this as a customer id for the whole billing system

So it's not really braintree specific, even if we make it match the one there.