LP#1708488: adjust how patron financial summary is exposed to checkout receipts

LP#1708488: adjust how patron financial summary is exposed to checkout receipts

This patch builds on the previous patch by grabbing the patron's
financial summary from the patron stats values. The "patron_money"
template value is no longer associated with a particular loan, meaning
that you can do things like this:

<span ng-if="patron_money.balance_owed">You owe the library ${{patron_money.balance_owed}}</span>

The additional values include

* patron_money.balance_owed - current balance
* patron_money.total_paid - payments made on outstanding fines/fees
* patron_money.total_owed - total of outstanding fines/fees

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>