Zipkin

[AyolaJayamaha]

Flipping zipkin chart on vertical axis would be done on the zipkin codebase. The zipkin codebase does not support date/time in milliseconds.

[JamesRTaylor]

Please squash all commits into a single commit.

[mujtabachohan]

Please merge with phoenix-tracing-webapp and name it phoenix-tracing. Use default properties for zipkin configuration in case they are not configurable.