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 
I found it strange myself. I followed the exception up the stack trace and it turns out the message is returned all the way to the Response objects from the models (horray)

On the flip side, I can leave the exception message i18n'd and ensure the log message is in English.