Use CRITICAL level for Sentry logging

[reginafcompton]

This PR turns down the volume on Sentry logging (from "WARN" to "CRITICAL"), like so:

'sentry': {
            'level': 'CRITICAL',
            'class': 'raven.handlers.logging.SentryHandler',
            'client_cls': OCDClient,
            'dsn': ******,
},

@fgregg - we decided to make this change, since the OCD channel in Semaphor has become overly cluttered with cannot resolve pseudo id warnings, and when the 4:00 pm aggressive scrapes begin, the Sempahor channel may become unusable.

[hancush]

to be clear, these errors will still show up in the scrape logs, so i will have something to consult, on the off chance a resolution error causes a problem tonight? if yes, happy to approve! we can turn it back up on monday.

[hancush]

(relatedly, are there other errors that won't be logged at this error level?)

[reginafcompton]

@hancush - yes, you should still see all the cannot resolve warnings in the logs (right at the end of each import)! I reverted back to the level we had before June 18.