Demote log messages and make `INFO` the default log level

Demote log messages that are URL-specific to the `DEBUG` log level.

This enables us to output more useful `INFO` messages without polluting the logs with unnecessary noise.

Also, make `INFO` the default log level and remove the `-debug` flag. As a consequence, the `-debug` flag is no longer necessary. `-verbose` will now show `DEBUG` messages and `INFO` log messages will be shown by default.

Notable examples of `INFO` messages include the AMQP and Redis
connection messages shown when the application initialises.