#178: add hint for unexpected exception to be reported to a developer

Author: Death111

src/main/java/de/doubleslash/keeptime/view/ExternalProjectsSyncController.java

@@ -482,7 +482,7 @@ protected List<HeimatController.HeimatErrors> call() {
             LOG.error("Task failed unexpectedly.", exception);
             loadingScreenShowSyncing("Something very unexpected has happened :(", loadingFailure);
 
-            showErrorDialog(Collections.singletonList("Error was:" + exception.getMessage()));
+            showErrorDialog(Collections.singletonList("Please report this to a developer. The error was:" + exception.getMessage()));
             showLoadingScreen(false);
             thisStage.close();
          });