Download xapi-gwt-api JAR file with all dependencies

All Gwt jre emulation code goes in this module, as well as any gwt-compiler overrides. xapi-gwt-api.jar must come before gwt-dev.jar on your compile classpath. A plugin is being built to automatically adjust maven runtime dependencies, but users of ant or IDEs will need to ensure the super jar comes before gwt-dev. We will petition gwt to accept our mods, but, until then, if you want bleeding edge features, you gotta do bleeding edge configuration. Code that ties directly into other modules, like java.lang.reflect for the reflection submodule, have their super-source here, and generators or other implementations in their own modules. This is to maintain consistency in what is or isn't whitelisted in XApi GWT. Some modules, like appengine, provide dependency-specific super-source in their own packages. This module is for jre, junit and core XApi services.