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
Probably anal, but these need to be finalif we are setting them only in the constructor.