Moves to zipkin 0.21

This moves to changes made in preparation of zipkin 1.0.

Here are the notables:

* Zipkin has autoconfiguration modules, where maven artifacts have the prefix 'zipkin-autoconfigure-X'
* Zipkin's ui now shares a version with everything else

* Zipkin now namespaces packages and configuration. ex zipkin.storage.X as opposed to zipkin.X
* All autoconfiguration classes are prefixed `Zipkin` to be easier to find

* Zipkin binds components like StorageComponent, as opposed to individual classes like SpanStore.
* Health checks are under the scope "zipkin" and broken down by component

* UI responsiveness is better by conditionally caching names queries for 5 minutes
* New `Collector` class, which makes logging and metrics patterns the same regardless of transport

spring-cloud-sleuth-samples/spring-cloud-sleuth-sample-zipkin-stream/src/test/java/example/ZipkinServerApplicationTests.java

@@ -7,7 +7,7 @@ import org.springframework.boot.test.IntegrationTest;
 import org.springframework.boot.test.SpringApplicationConfiguration;
 import org.springframework.test.context.ActiveProfiles;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
-import zipkin.SpanStore;
+import zipkin.storage.StorageComponent;
 
 import static org.junit.Assert.assertEquals;
 
@@ -18,11 +18,11 @@ import static org.junit.Assert.assertEquals;
 public class ZipkinServerApplicationTests {
 
 	@Autowired
-	private SpanStore store;
+	private StorageComponent storage;
 
 	@Test
 	public void contextLoads() {
-		int count = this.store.getServiceNames().size();
+		int count = this.storage.spanStore().getServiceNames().size();
 		assertEquals(0, count);
 	}