Add WorkItem model for Problem sheets and equivalent

test/fixtures/work_items.yml

@@ -0,0 +1,11 @@
+# Read about fixtures at https://api.rubyonrails.org/classes/ActiveRecord/FixtureSet.html
+
+one:
+  title: MyString
+  course: one
+  due_date07/10/2023: MyString
+
+two:
+  title: MyString
+  course: two
+  due_date07/10/2023: MyString

test/models/work_item_test.rb

@@ -0,0 +1,7 @@
+require "test_helper"
+
+class WorkItemTest < ActiveSupport::TestCase
+  # test "the truth" do
+  #   assert true
+  # end
+end