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 (closed), #819 (closed)