unique_id: Use IFA, IFV and auto generated fallback

* If IFA is available, use it
* If IFV is available, use it
* Then, fallback to an auto generated UUID

Use `LIQUID_USE_IFA=1` in Preprocessor Marcos (at Build Settings) to use IFA.

Signed-off-by: Miguel M. Almeida <miguelcma@CMA-Retina.local>
Update version to 0.5.1-beta

Signed-off-by: Miguel M. Almeida <miguelcma@CMA-Retina.local>