Improve group changing, update instance on version change

Gives a list of existing groups to choose from.
Instances are updated as long as there is at least one valid account.

logic/OneSixUpdate.cpp

@@ -54,11 +54,9 @@ void OneSixUpdate::executeTask()
 
 	if (m_only_prepare)
 	{
-		if (m_inst->shouldUpdate())
-		{
-			emitFailed("Unable to update instance in offline mode.");
-			return;
-		}
+		/*
+		 * FIXME: in offline mode, do not proceed!
+		 */
 		setStatus("Testing the Java installation.");
 		QString java_path = m_inst->settings().get("JavaPath").toString();