support open-tracing API.

@rayzhang0603 , in 2.1-2017, we provide opentracing-implemetation tracer. Have tested by using motan's filter, with your source code, since your next version is not released yet.

Seem passed. The visualization is above. 

btw @andot , I think this feature will work in hprose-java filter. `opentracing-contrib/java-hprose` is in releasing. 

Remove the over-design about methodMatcher, use byte-buddy judge instead. Add module ‘skywalking-toolkit-opentracing-activation’ ( no activation implementation ).

use ‘%T’ instead of ‘%x’, to avoid log4j NDC failure. https://github.com/wu-sheng/sky-walking/issues/77

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