added model '_meta' field support (PY-561)

python/src/com/jetbrains/python/psi/types/PyClassMembersProvider.java

@@ -17,4 +17,6 @@ public interface PyClassMembersProvider {
   Collection<PyDynamicMember> getMembers(PyClass clazz);
   @Nullable
   PsiElement resolveMember(PyClass clazz, String name);
+
+  boolean hasUnderscoreWildCard(String name);
 }

python/src/com/jetbrains/python/psi/types/PyClassType.java

@@ -136,7 +136,7 @@ public class PyClassType implements PyType {
     for (PyClassMembersProvider provider : Extensions.getExtensions(PyClassMembersProvider.EP_NAME)) {
       for (PyDynamicMember member : provider.getMembers(myClass)) {
         final String name = member.getName();
-        if (underscore_filter.value(name)) {
+        if (underscore_filter.value(name) || provider.hasUnderscoreWildCard(name)) {
           ret.add(LookupElementBuilder.create(name).setIcon(member.getIcon()).setTypeText(member.getShortType()));
         }
       }