Adding a number of logging messages for verification process.

Simply adding a number of logging messages in at the info / warn / error level.

* Any exceptions raised will be logged as well
* Info level messages to catch entry points of verification flow
* Info level messages for verification approve / deny
* Already good info level messages for purchase callbacks in place.

@wedaly @rlucioni @dianakhuang 
Is there a reason this log message is marked for translation? It doesn't look like any other log messages added here are marked for translation.