QmlJS: Lazy-load console items to allow for recursion

Using Utils:TreeView automatically gives us the capability for loading
item as they are expanded. This way we can show recursive structure in
the console as well as load data from the debug server on demand.

Also, properly print error messages received from unsuccessful
command evaluations.

Task-number: QTCREATORBUG-14931
Change-Id: I66d440eedd9723b04670169b27db1ee18f3f2891
Reviewed-by: hjk <hjk@theqtcompany.com>

src/plugins/debugger/qml/qmlv8debuggerclientconstants.h

@@ -105,6 +105,8 @@ const char REFS[] = "refs";
 const char BODY[] = "body";
 const char NAME[] = "name";
 const char VALUE[] = "value";
+const char SUCCESS[] = "success";
+const char MESSAGE[] = "message";
 
 const char OBJECT[] = "{}";
 const char ARRAY[] = "[]";