Shell wrapper to source env before running command

Usage: (you need to have `.env` file to use this)

```bash
$ bin/run ./manage.py shell
```

If you want to check that it in fact applied correct settings:
```bash
$ bin/run ./manage.py check_settings
```

Can be used to run migrations:
```bash
$ PYTHONPATH=. bin/run python migrations/...some migration...
```