This updates to the latest release. Beyond bug fixes, there are some
notable changes:
* storage: writes are now via AsyncSpanConsumer
* storage: added elasticsearch
* zipkin-ui: constrains start time to look for traces
* zipkin-ui: assets set cache headers, increasing responsiveness
* core: debug logging available for zipkin.internal.DependencyLinker
Zipkin 0.4.1 obviates some duplication of configuration. It is also the
first version that's published as a docker image.
By switching to the published image of zipkin-java, we can be more
consistent, as `spring-cloud-sleuth-zipkin-stream` is derived from that,
not the scala query service.
Recent versions of zipkin and brave operate with http instead of scribe.
This changes the implementation accordingly, as well adds a sampler to
the POST endpoint.
A notable impact is that we no longer require a collector process, as
the zipkin server's POST endpoint is a collector.
