bug 858360 initialize the SentryHandler for Raven >= 3.0
* Got rid of the alternate MetlogTastypieHandler and just use the
  standard SentryHandler with a client extracted from
  raven.contrib.django.models
* dropped USE_METLOG_FOR_TASTYPIE as tastypie will now just use
  whatever sentry client is defined by settings.SENTRY_CLIENT