Make GQ server side not depends on gwt-servlet not gwt-dev

Adding org.json dependency since we depend on it, and 2.7
uses a rebased version of android.json. We will have this
dependency in snapshot until we replace json usage in server
side, but we have to remove before releasing gquery.
Yes it's reliable, if the user does not deploy any gwt-xx.jar in server side, this check will not find the GWT class, that absolutely means that this code is being executed in JVM, so we return jre implementations. Otherwise If the jars are in server side, this code will find GWT and GWTBridge, so it asks in the formal way to GWT if the code is running as dev mode. Tests are passing for gwt and dev modes, which means that it selects the appropriate factory when gwt jars are in the classpath. I have this solution working in a project without any gwt nor vaadin dependency.