- Introduces a new `vpn` app with the following models:
- Tunnel
- TunnelTermination
- IKEProposal
- IKEPolicy
- IPSecProposal
- IPSecPolicy
- IPSecProfile
* 12794 change User ref to get_user_model
* 12794 call get_user_model once in tests
* 12794 call get_user_model once in tests
* 12794 use settings.AUTH_USER_MODEL for FK reference