Trim whitespace
Treat SENTRY_DSN like other envvars

For whatever reason we were reading SENTRY_DSN out of the enviroment
differently than other variables.
Beef up Sentry logging

 - use `level` properly (replaces 5xx-style response codes)
 - use `response code` tag for full response code (500, not 5xx)
 - fold non-Response exceptions under 500
 - tag with username