Refactor and extend NAS Registration Request

Extended NAS Registration Request generation and encoding according to
8.2.6 of 3GPP TS 24.501. Main topics:

- NAS Registration Type
- NAS KSI
- integrity protection
- NAS container encoding

Improvements:

- Add 5GMM Modes in NAS
- Introduced 5GMM state machine

Fixes:

- add 5GMM Capability IE to Registration Request
- closes #881, #819