Integrate SkyBiometryFaceRecognition

### Need
PyBetaFace API gives very poor results:

- When it should recognize Andrei: 

```bash
INFO: Received matches from BetaFace: {'diana@amilab.ro': 0.606, 'andrei@amilab.ro': 0.594, 'alin@amilab.ro': 0.603}
INFO: Out of the matches returned by BetaFace, the maximum confidence is only 0.61 (should have been at least 0.75)
```

- When it should recognize Diana:

```bash
INFO: Received matches from BetaFace: {'diana@amilab.ro': 0.7}
INFO: Out of the matches returned by BetaFace, the maximum confidence is only 0.70 (should have been at least 0.75)
```

### Solution

Starting from this, we investigated other solutions for Face Recognition module and stopped at [SkyBiometry](https://www.skybiometry.com/)

I have already added the client library for SkyBiometry in #216 

SkyBiometrics limits for free subscription:

```python
hourly: 100 calls
daily: 5000 calls
monthly: 5000 calls
trained faces: 1000 faces trained
```

Results:

```bash
Recognizing andrei...
[{u'confidence': 72, u'uid': u'andrei@amilab-test2'},
 {u'confidence': 51, u'uid': u'diana@amilab-test2'}]

Recognizing diana...
[{u'confidence': 100, u'uid': u'diana@amilab-test2'},
 {u'confidence': 48, u'uid': u'andrei@amilab-test2'}]
```

#### TODO
- [ ] find a satisfying management of both PyBetaFace and SkyBiometry in turns for face recognition
- [ ] train SkyBiometry with all amilab members (Alin + Cosmin + Liviu)
- [ ] make calls to SkyBiometry in FaceRecognition PDU
- [ ] assert all tests (pipeline+unit+integration) are passing with flying colors :tada: