Add skeleton for question types

lib/diskuy/question/multiple_choice_answer.ex

+defmodule Diskuy.Question.MultipleChoiceAnswer do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+end

lib/diskuy/question/multiple_choice_question.ex

+defmodule Diskuy.Question.MultipleChoiceQuestion do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+end

lib/diskuy/question/short_answer_answer.ex

+defmodule Diskuy.Question.ShortAnswerAnswer do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+end

lib/diskuy/question/short_answer_question.ex

+defmodule Diskuy.Question.ShortAnswerQuestion do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+end

lib/diskuy/question/true_false_answer.ex

+defmodule Diskuy.Question.TrueFalseAnswer do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+end

lib/diskuy/question/true_false_question.ex

+defmodule Diskuy.Question.TrueFalseQuestion do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+end

lib/diskuy/question/upload_file_answer.ex

+defmodule Diskuy.Question.UploadFileAnswer do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+end

lib/diskuy/question/upload_file_question.ex

+defmodule Diskuy.Question.UploadFileQuestion do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+end