The create_command command should create the command structure inside the application dir

If the app which we're creating a command structure directory for isn't located in the project directory, the command does create a blank directory with the app's name inside the project directory, then install the command directory structure in there.

For example:
```
~ mkdir apps
~ touch apps/__init__.py
~ python manage.py create_app -p apps sample_app
# add 'apps.sample_app' to settings.py
~ python manage.py create_command -n sample_command sample_app
~ find .
.
./apps
./apps/__init__.py
./apps/sample_app
./apps/sample_app/__init__.py
./apps/sample_app/forms.py
./apps/sample_app/models.py
./apps/sample_app/urls.py
./apps/sample_app/views.py
...
./sample_app
./sample_app/management
./sample_app/management/__init__.py
./sample_app/management/commands
./sample_app/management/commands/__init__.py
./sample_app/management/commands/sample_command.py
```

With this change, the create_command command creates the new command structure directory in the correct place (like the create_jobs command, which already behaves correctly)


EDIT: second pull request was merged in to add a create_template_tags management command.