fixed the gradle wrapper

added the bootstrapper jar again and removed the duplicate wrapper from the library submodule

http://www.gradle.org/docs/current/dsl/org.gradle.api.tasks.wrapper.Wrapper.html:

	The scripts generated by this task are intended to be committed to your version control system. This task also generates a small gradle-wrapper.jar bootstrap JAR file and properties file which should also be committed to your VCS. The scripts delegates to this JAR.