Extract latent from clustering models

[WenjieDu]

What does this PR do?

Fixing #177

Before submitting

• This PR is made to fix a typo or improve the docs (you can dismiss the other checks if this is the case).
• Was this discussed/approved via a GitHub issue? Please add a link to it if that's the case.
• I have commented my code, particularly in hard-to-understand areas.
• I have written necessary tests and already run them locally.

[coveralls]

Pull Request Test Coverage Report for Build 6308606458

• 33 of 34 (97.06%) changed or added relevant lines in 2 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.5%) to 83.625%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pypots/clustering/crli/model.py	11	12	91.67%

Files with Coverage Reduction	New Missed Lines	%
pypots/clustering/vader/model.py	1	88.57%
pypots/clustering/crli/model.py	2	93.33%

Totals
Change from base Build 6308599763:	0.5%
Covered Lines:	3585
Relevant Lines:	4287

---

💛 - Coveralls