Download xapi-gwtc-impl JAR file with all dependencies

This module contains the business logic of running gwt compiles. It implements and exposes all functionality of the gwt compiler, and should only ever be included in dev-mode runtimes that need to perform gwt compiles. In the maven plugin, the jre frontend and this backend are used together in one runtime. In the collide plugin, the gwt frontend runs in the browser, and this backend runs in vert.x server.