Script to synchronize payments with a CSV

Adds a management script which takes a csv file name argument. Based on the values in the associated csv, transactions are deleted and fund amounts are updated.

Adds timezone configuration info (though we encourage UTC for everything).

Uses `round` when multiplying to turn dollars into cents to avoid annoying floating point issues.
I would have thought that this file would be named "test_sync_payments.py" to line up with the file it's testing, although I'm less familiar with our naming conventions