Changes following review
- Reusing CounterService to automatically profit from Dropwizard if present
- NoOp is the default impl for SpanReporterService
- SpanReporterService has configurable metric names (it's enough to change the
name to 'meter.a.b.c' to profit from Dropwizard's meters)
Fixes gh-99
- Changed Random instantiation to a shared Random
- Changed the name of the converter
- Changed generator into random
- Span id is now non-nullable.
- it gets generated in the http filter if it's not there
- it's generated in the spring-integration channels if it wasn't set
It's not really necessary to use rabbit, but the existing tests
weren't really using the stream components at all because
zipkin spans were being collected by spring-cloud-sleuth-zipkin.
