Remove dependency on opentracing-concurrent

[pavolloffay]

opentracing-concurrent is used in tests therefore should be removed from opentracing-jaxrs2

[pavolloffay]

I think we can depend on this jar as it's need when working with async client api

[sjoerdtalsma]

Maybe it's an idea to split up client and server support as these both have very different dependencies?

edit Just noticed my issue #16 😄