fix clean_media command, add REST API, start Angular front example

requirements.txt

uploadexample/api/__init__.py

uploadexample/api/apps.py

uploadexample/api/serializers.py

uploadexample/api/urls.py

uploadexample/api/validators.py

uploadexample/api/views.py

uploadexample/upload/admin.py

uploadexample/upload/management/commands/clean_media.py

uploadexample/upload/models.py

uploadexample/upload/static/css/registration.css

uploadexample/upload/templates/upload/base.html

.../templates/upload/studentregistration_confirm_delete.html

...ple/upload/templates/upload/studentregistration_form.html

...ple/upload/templates/upload/studentregistration_list.html

uploadexample/upload/tests.py

uploadexample/upload/urls.py

uploadexample/upload/views.py

uploadexample/uploadexample/settings.py

uploadexample/uploadexample/urls.py