Align dockerization process with spring.io guides

(And with existing Spring Cloud projects.) Uses a maven plugin to
build the image. It can be pushed manually, or else using
-Ddocker.image.prefix=<path_to_repo>. Removes some of the hard-coded
host names and stuff that came with the old version.

spring-cloud-stream-module-launcher/docker-compose.yml

@@ -0,0 +1,19 @@
+redis:
+  image: redis
+
+timesource:
+  image: springcloud/stream-module-launcher
+  links:
+    - redis
+  environment:
+    SPRING_REDIS_HOST: redis
+    MODULES: org.springframework.cloud.stream.module:time-source:1.0.0.BUILD-SNAPSHOT
+
+logsink:
+  image: springcloud/stream-module-launcher
+  links:
+    - redis
+  environment:
+    SPRING_REDIS_HOST: redis
+    MODULES: org.springframework.cloud.stream.module:log-sink:1.0.0.BUILD-SNAPSHOT
+