Use a Timbre appender to send errors to Sentry instead of calling the Sentry API directly

[djwhitt]

This would tidy up the code slightly and should make it easier to swap error reporters in the future. It also removes a dependency from the event router which will help with running it in other environment and potentially extracting it in the future.

[djwhitt]

Details about writing appenders can be found here: https://github.com/ptaoussanis/timbre#configuration