Emit metric for excessive operation names instead of rejecting the span

[LakerBaker]

The code that rejects spans when a service submits too many operation names is causing problems, particularly without the ability to override service name with a tag (see opentracing/specification#131). Instead of rejecting spans, the code will emit a metric so that offending services can be notified of the issue.

[LakerBaker]

With #65 and a couple of prior PRs all operation name counting logic is removed. We're building a better throttling system and until that is developed we will do this checking in an internal Expedia-specific package. Closing.