Make zipkin-web dist file runnable

With this patch you can run zipkin-web with "java -cp libs/ -jar zipkin-web-1.2.0-SNAPSHOT.jar -zipkin.web.resourcesRoot=resources/" from /zipkin-web/dist/zipkin-web. Without this patch zipkin-web can't resolve its resources. 

This is useful when you want to run zipkin-web without going through sbt.