NBI Component - IETF Network plugin:

- Added missing YANG data models
- Updated build-yang-bindings.sh script
- Corrected unitary test test_ietf_network.py
- Reorganized message composer scripts
- Removed unneeded code files
- Implemented composition of nodes, links, termination points, and networks
- Implemented manual fixes for what pyangbind does not support
- Added NameMapping class to cache entity names