GH-65: Add polled-consumer Sample

Resolves https://github.com/spring-cloud/spring-cloud-stream-samples/issues/65

Polishing - PR Comments

- add docker-compose
- change runner to process multiple messages

processor-samples/polled-consumer/.gitignore

@@ -0,0 +1,24 @@
+target/
+!.mvn/wrapper/maven-wrapper.jar
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+
+### NetBeans ###
+nbproject/private/
+build/
+nbbuild/
+dist/
+nbdist/
+.nb-gradle/