loaddemo: fix copying files from demo/media.

If demo files are placed in first-level subdirectories of the media
directory, they were not being copied correctly when loading the demo.
For example, "demo-files/media/ethics/Ethics_Approval_....txt" was
incorrectly copied as "media/ethics" rather than
"media/ethics/Ethics_Approval_....txt".

Additionally, ensure that the destination directories are created if
they don't already exist.

physionet-django/user/management/commands/loaddemo.py

@@ -99,13 +99,15 @@ def copy_demo_media():
     for subdir in os.listdir(demo_media_root):
         demo_subdir = os.path.join(demo_media_root, subdir)
         target_subdir = os.path.join(settings.MEDIA_ROOT, subdir)
+        os.makedirs(target_subdir, exist_ok=True)
         for item in [i for i in os.listdir(demo_subdir) if i != '.gitkeep']:
             path = os.path.join(demo_subdir, item)
             if os.path.isdir(path):
                 shutil.copytree(os.path.join(demo_subdir, item),
                                 os.path.join(target_subdir, item))
             else:
-                shutil.copy(path, target_subdir)
+                shutil.copy(os.path.join(demo_subdir, item),
+                            os.path.join(target_subdir, item))
 
     # Published project files should have been made read-only at
     # the time of publication