No longer persist XModule templates

Instead, we use XModule field default values when creating an empty
XModule. Driven by this use case, we also allow for XModules to be
created in memory without being persisted to the database at all. This
necessitates a change to the Modulestore api, replacing clone_item with
create_draft and save_xmodule.

lms/djangoapps/instructor_task/tests/test_base.py

@@ -119,7 +119,7 @@ class InstructorTaskModuleTestCase(LoginEnrollmentTestCase, ModuleStoreTestCase)
 
         # add a sequence to the course to which the problems can be added
         self.problem_section = ItemFactory.create(parent_location=chapter.location,
-                                                  template='i4x://edx/templates/sequential/Empty',
+                                                  category='sequential',
                                                   display_name=TEST_SECTION_NAME)
 
     @staticmethod
@@ -169,7 +169,7 @@ class InstructorTaskModuleTestCase(LoginEnrollmentTestCase, ModuleStoreTestCase)
                         'num_responses': 2}
         problem_xml = factory.build_xml(**factory_args)
         ItemFactory.create(parent_location=self.problem_section.location,
-                           template="i4x://edx/templates/problem/Blank_Common_Problem",
+                           category="problem",
                            display_name=str(problem_url_name),
                            data=problem_xml)
 

lms/djangoapps/instructor_task/tests/test_integration.py

@@ -243,7 +243,7 @@ class TestRescoringTask(TestIntegrationTask):
                                         grader_payload=grader_payload,
                                         num_responses=2)
         ItemFactory.create(parent_location=self.problem_section.location,
-                           template="i4x://edx/templates/problem/Blank_Common_Problem",
+                           category="problem",
                            display_name=str(problem_url_name),
                            data=problem_xml)
 
@@ -293,7 +293,7 @@ class TestRescoringTask(TestIntegrationTask):
             # Per-student rerandomization will at least generate different seeds for different users, so
             # we get a little more test coverage.
             ItemFactory.create(parent_location=self.problem_section.location,
-                               template="i4x://edx/templates/problem/Blank_Common_Problem",
+                               category="problem",
                                display_name=str(problem_url_name),
                                data=problem_xml,
                                metadata={"rerandomize": "per_student"})