fixes #226. allow launched applications to signal the launcher's job is complete by returning Continue

launch/interface/src/main/java/xsbti/Continue.java

@@ -0,0 +1,5 @@
+package xsbti;
+
+/** A launched application returns an instance of this class in order to communicate to the launcher
+* that the application's main thread is finished and the launcher's work is complete, but it should not exit.*/
+public interface Continue extends MainResult {}