ThreadLocal context propagation for DataFetcher's

The WebMvc starter now supports propagation of ThreadLocal values
extracted at the level of the HTTP handler.

Closes gh-53

samples/webflux-websocket/src/main/java/io/spring/sample/graphql/ContextWebFilter.java

@@ -23,9 +23,9 @@ import org.springframework.web.server.WebFilterChain;
 
 /**
  * WebFilter that inserts a key-value pair into the Reactor context which is
- * transferred to and accessible to Reactor-based data fetchers.
+ * transferred to and accessible in Reactor data fetchers.
  */
-public class ReactorContextWebFilter implements WebFilter {
+public class ContextWebFilter implements WebFilter {
 
 	@Override
 	public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {

samples/webflux-websocket/src/main/java/io/spring/sample/graphql/SampleApplication.java

@@ -28,8 +28,8 @@ public class SampleApplication {
 	}
 
 	@Bean
-	ReactorContextWebFilter reactorContextWebFilter() {
-		return new ReactorContextWebFilter();
+	ContextWebFilter reactorContextWebFilter() {
+		return new ContextWebFilter();
 	}
 
 }