Several Enhancements and bug fixes

- Completely decoupled SF and SFC.
- Completely decoupled SFP and SFC
- SFC is just a blueprint to build SFPs
- SFC can be deleted and SFPs stay
- If SF is deleted/updated, SFPs/SFF
  are deleted/updated accordingly
- Enhanced REST API
- All APIs are using reflection and factories.
  Meaning API implementation can be changed without changing signature
- Hardening of the code
- Modified Yang models by introducing operational containers.
- Fixed concurrency issue.

Change-Id: I8478b4ce3b0d2ab3092b5458fcd09116b6b1664f
Signed-off-by: Reinaldo Penno <rapenno@gmail.com>