add for_answer column on questions, resolve type with it

last type is PrivatePost

db/migrations/20180831165621_question_for_answer.js

+
+exports.up = async function(knex, Promise) {
+    await knex.schema.table('questions', table => {
+        table.string('for_answer', 128);
+    });
+};
+
+exports.down = async function(knex, Promise) {
+    await knex.schema.table('questions', table => {
+        table.dropColumn('for_answer');
+    });
+};

src/graphql/resolvers/messages.js

@@ -16,8 +16,10 @@ const MessageResolvers = {
             if (obj.for_question) {
                 return "Answer";
             }
-            return "Question";
-
+            if (obj.for_answer) {
+                return "Question";
+            }
+            return "PrivatePost";
         }
     },