AWS-S3: Close tag in the sample config

PR: https://github.com/spring-projects/spring-integration-extensions/pull/85
Splunk: Populate `count=0` to the reader `Job`

PR: https://github.com/spring-projects/spring-integration-extensions/pull/82
DSL: Use `DelayerEndpointSpec` for `.delay()`

GH: https://github.com/spring-projects/spring-integration-extensions/issues/84
Kafka: KCCtx: return null if consumedData.isEmpty

Fixes: https://github.com/spring-projects/spring-integration-extensions/issues/68
Add the Spring IO plugin to Splunk extension

Configure the Spring IO plugin such that it's only applied when the
build is run with -PplatformVersion=<version>. This platformVersion
property is used to determine the version of the Platform that will
be used when running the springIoCheck task. The plugin can be used
by running a build as follows:

./gradlew clean springIoCheck -PplatformVersion=1.1.0.BUILD-SNAPSHOT -PJDK7_HOME=… -PJDK8_HOME=…

This will test the project on JDK7 and JDK 8 using the dependencies
defined in the latest snapshot of Spring IO Platform 1.1.0.