Polish SI test binder after maven publishing

- Renamed classes and package to be consistent with the intentions of this binder (e.g., TestChannelBinder, TestChannelBinderConfiguration etc)
- Added package-info.java

Resolves #1241

spring-cloud-stream-binder-test/pom.xml

@@ -38,5 +38,11 @@
 			<artifactId>spring-boot-starter-test</artifactId>
 			<scope>compile</scope>
 		</dependency>
+		<dependency>
+			<groupId>org.springframework.cloud</groupId>
+			<artifactId>spring-cloud-stream</artifactId>
+			<type>test-jar</type>
+			<classifier>test-binder</classifier>
+		</dependency>
 	</dependencies>
 </project>