CORDA-650: Eliminate unnecessary dependency on "graphstream" library (#1732)

This library has one usage in ClientRPC example and:
* Uses Scala 2.10 - which is quite dated
* Has a transitive dependency on JUnit

docs/source/example-code/build.gradle

@@ -39,6 +39,7 @@ dependencies {
     compile "org.graphstream:gs-core:1.3"
     compile("org.graphstream:gs-ui:1.3") {
         exclude group: "bouncycastle"
+        exclude group: "junit"
     }
 
     cordaCompile project(path: ":node:capsule", configuration: 'runtimeArtifacts')