Improve error logging in sentry for celery workers.
Merge pull request #35 from pmclanahan/better-error-logging

Improve error logging in sentry for celery workers.
Fix exceptions when no welcome requested and text format.

Sentry showed us exceptions in the update_user task
were being caused when no welcome was requested and
the email format was set for text. This is because
welcome would be None, yet we still tried to append
'_T' to it. DOH!
Fix issue when unsubscribing from all newslettes.
Capture args and kwargs sent to tasks when they error.

And send this information to Sentry. This is instead of
just logging the exception.
Fix excess logging.
Merge pull request #38 from pmclanahan/capture-task-args-in-exceptions

Capture args and kwargs sent to tasks when they error.
Remove manual sentry logging.

It was duplicating what the celery helper was
doing, and not even as well. It was also masking
the source of the real errors.