XD-1306: Move ftp support from .x package to spring-xd-dirt batch package

* Created spring-xd-extension-batch project and moved RemoteFilePartitioner and RemoteFileToHadoopTasklet from spring-xd-dirt to the new project.  
* Removed spring-integration-file and spring-integration-ftp from the dirt dependencies
* Moved BusTestUtils to spring-xd-test, since now shared by spring-xd-dirt and spring-xd-extension-batch
* Added Integration Test for ftphdfs
* Upgrade to Gradle 1.12  

To avoid installing every hadoop distribution ftphdfs/lib, introduced https://github.com/spring-projects/gradle-plugins/blob/master/propdeps-plugin to support provided dependencies.  This required an update to gradle 1.12, which has some known issues with intellij